It’s worth doing your homework whether you are preparing to sell at auction or buy. One of the most important reasons is provenance. This is the history of ownership of an item. The more significant it is, the better, and if you can trace it back through solid documentary evidence to the point of its creation, all the better.

Many and varied are the tales of people who let something go for a song only to discover later that it was worth a small fortune. By the same token, experts and others who have bothered to investigate things that turn up in saleroom catalogues properly can snap up a bargain.

So what is the best advice to follow when confronted by a lot that piques your interest?

If possible – and this is often not the case now, thanks to the internet and access to auctions on a global basis – go to the view and look at the item in person.

Ask yourself a few questions? Does it look like the real deal? Does the estimate reflect its value? If you look past the flaws, damage etc, does the quality really shout out from beneath?

If you are an expert in your field, it’s true that first impressions really do count. You may immediately recognise the typical motifs or style of an artist that others have missed; or you may also spot that something isn’t quite right and the mark and period Qianlong vase you hankered after is actually a later copy.

One of my favourite examples of close inspection paying off was a set of daguerreotypes – one of the earliest forms of photographic development – that came up for auction a number of years ago. Taken in Italy, France and Switzerland in the mid 19th century, they were attractive but pitched at no more than £80. They sold for £75,000, but, as it turned out, were worth a great deal more because it transpired that they were the lost images of John Ruskin’s European tour. As the pre-eminent art critic of the 19th century, Ruskin was fascinated by the art and architecture of places such as Venice and was one of the first to catch them in photographs. Although it took the eye of a Ruskin specialist to spot the link, the discovery was a sensation and the previously unknown images were later published in a book.

So, one of the reasons that auctions continue to prove so popular is that on occasion they can be a bit like winning the lottery.

Watching the Antiques Roadshow recently, I was reminded of the most important question a professional should ask when valuing something: why are you having it valued? This is because valuations will differ depending on the answer.

This might sound a little odd, but it’s logical, if you think about it. Let’s consider a diamond ring, for instance. If you want it valued for insurance purposes, you are going to need enough cover to replace it at retail cost. If you want it valued for sale at auction or to a dealer, the valuer will consider what a dealer might pay for it, so that they can add enough profit on to it to make it worthwhile buying for resale. In general, the insurance valuation in this case would be around four times the resale value at auction or to a dealer. That accounts for production costs, retail costs and the retail profit of the replacement ring.

Probate is another scenario. In that instance, a valuer is likely to provide a value on the low side, which is still realistic. So, it is possible to have four different values for the same item, all of which are valid.

This is why, for the most part, when you watch the Roadshow these days, the experts will specify how they are valuing what you present them with. “You could expect to get X at auction”, or “You should insure this for Y”, they will say. Anyone who simply says “It is worth X” is not really being much help unless they qualify the statement by explaining the circumstances of the valuation.

Another commonplace query when people consign items for auction concerns the reserve. This is the price below which the item will not be sold, to protect the seller from losing out. It is different from the estimate, which is made public and is the price range within which the item is expected to sell. Quite often the reserve will be fixed at the low estimate. Under English law it can’t be higher than the low estimate as that would be misleading potential buyers into thinking they could acquire it at the low estimate.

Pricing a piece for auction can be a tricky business in the same way that pricing a house for sale is. Make the estimate too high and you put off buyers; make it too low and you may annoy the consignor, while giving potential bidders an unrealistic impression of what it is worth – and that can be damaging for an auctioneer’s reputation.

Those who price their homes correctly for sale can attract a high number of viewings resulting in competition that puts the prices up as part of a bidding war. The same is true for chattels auctions, where the ideal price guide is one that remains within the realistic range of an item’s value but is low enough to entice bidders.

The system of British hallmarks dates back a few centuries, but the concept of hallmarking dates back thousands of years, to the time when coins first emerged as currency. Individually stamped by local officials, those early coins would have been made of electrum (a mix of gold and silver) or silver, and the stamp would denote the purity of the metal, which in turn attested to its value. It was much later that base metal coins represented far greater values, effectively acting as tokens rather than carrying their actual value in their make-up.

From the earliest times one of the problems with currency losing its value was the clipping of coins, where the unscrupulous would harvest minute amounts of silver from the edge of individual coins stamped for a specific value. Eventually they would have enough silver to either mint new coins or make other valuable items. However, this also meant that the currency in circulation depreciated in value. The authorities put a stop to this trick in the reign of Charles II by introducing lettering around the edge of coins.

If debasement of the coinage – as even happened officially under Henry VIII to save money – was an age-old problem, so was debasement of objects made from precious metals. How did you know that the ring or goblet you bought was pure gold or silver, and not made from something cheaper, mixed in with a little of the precious metal to give it the appearance of something more valuable?

In England, King Edward I started to tackle the problem by introducing a law in 1300 making it compulsory for all silver objects to meet a sterling silver standard of 92.5% purity. To ensure this, he ordered that objects passing an official test or ‘assay’ should be marked with a leopard’s head.

Edward’s grandson, Edward III, granted a charter to the Worshipful Company of Goldsmiths 27 years later, and all objects made from gold had to be sent to the Goldsmiths’ Hall in London for assaying and approval. Hence the word ‘hallmark’.

Regional assay offices in England for silver were set up later in Sheffield, Birmingham, York, Exeter, Newcastle upon Tyne, Norwich and Chester. In Scotland, Edinburgh and Glasgow had assay offices, and in Ireland there was an office in Dublin. Sheffield, Birmingham, Edinburgh and Dublin survive. Of the others, some (Chester and Glasgow) lasted well into the 20th century, while others (Norwich, closed 1702) have been long gone.

This time of year is what the media call the Silly Season, traditionally a period when news is thin on the ground and reporters will file copy on bizarre tales that wouldn’t normally make it into print. They do this because many newspapers and news websites are working on skeleton staff during the holidays and are under more pressure to fill the space available. It’s an ideal time to look out for articles on the weird and wonderful things that have sold at auction.

I recently trawled through the archives with this in mind and here are a few of things I came up with:

• William Shatner’s kidney stone. That’s right, in 2006 the Starship Enterprise’s former Captain Kirk raised $25,000 for charity with this tasteless offering.
• A grandmother. Ten-year-old Zoe Pemberton put her grandma, Marion Goodall, up for auction on eBay in 2010. The site shut the sale down when the price reached £20,000.
• Lee Harvey Oswald’s coffin. After JFK’s assassin was exhumed in 1981 to check that a body double had not been buried in his place, he was reburied in a new coffin. The original one fetched nearly $90,000.
• New Zealand. In 2006 an Australian man set a starting pricing of one Australian cent for the country. eBay also closed down this sale… when bidding reached Aus$3,000.

While it may be the Silly Season, it is also the approach of the Grouse Season. This is an area of pheasant shoots, and while those ready to take aim will have to wait until October 1 for that, August 12 is the start of the Red Grouse season.

While blasting birds out of the sky has never been my passion, the paintings of game birds by Archibald Thorburn are. His depictions of pheasant, grouse and ptarmigan are pre-eminent among British bird painters of the past century, as prices at auction will confirm. A decent watercolour of any of these birds in a moorland setting will have no problem encouraging bids up to the £25,000 mark.

Collectors have long taken aim at Thorburn, but I suppose he really came into his own when the popularity of shooting spread from the landed gentry to commercial shoots in the 1980s.

Born the son of a miniaturist painter who worked for Queen Victoria near Edinburgh in 1860, Thorburn had little to no formal training except for a brief stint at art school in St John’s Wood. What really set him on the road to his life’s work was a stroke of luck. In 1887 when the Dutch artist J.G. Keulemans fell ill, Thorburn took over the commission from Lord Lilford of Northampton to complete the illustrations for the seven-volume Coloured Figures of the Birds of the British Islands. By the time he finished his career had taken flight.