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Jackie Coulter, head of sothebys.com Europe, told the Antiques Trade Gazette that they should be able to prove their ability to sell high value art within four or five weeks.

Such is their confidence in the future performance of the online auction service that they have already pledged themselves to publishing sale results, although exactly how this will be done has yet to be worked out. If Sotheby's do publish full sale results – especially if they prove successful – it will be a significant step in boosting public confidence in the value of online auctions; just as significantly, it will force competitors to follow suit and open up the market to analysis.

Online sales on sothebys.com will take two forms: lots consigned by associate dealers – approved dealers invited by Sotheby's to post their own stock on the site for sale – can be added as and when the dealer sees fit; lots consigned by Sotheby's clients will be sold over set sale periods of between two and four weeks.

Associate dealers put up their own catalogue descriptions and guarantee their own lots, while lots consigned via Sotheby's must be delivered to the auction house for assessment by inhouse experts. Of the 5000 lots offered on the site at the launch, about half were put on by 400 associate dealers and half by Sotheby's themselves.

A successful bidder who is dissatisfied with the goods on delivery would first contact the vendor (the dealer if it is an associate dealer, Sotheby's if it is not). Sotheby's would act as a final arbitrator if an associate dealer failed to give satisfaction and, as Sotheby's European chief executive Robin Woodhead stressed, this process would be rigorously policed. After all, this assurance is as important for confidence in the service as the Sotheby's brand itself. From a legal point of view, the auction site and dealer contracts are subject to New York State law.

Just as interesting will be to see how far Sotheby's take the online business. No-one is certain yet whether sales at the podium will gradually give way to the Web (the official line is they will not suffer by comparison), but there are bound to be certain low value antiques and collectables that lend themselves more easily to online auctions as a rule.

No-one expects the top value prestige lots ever to be sold online, as there is nothing so profile raising as a dramatic round of bidding for a Van Gogh in front of TV cameras in the saleroom. In addition, running an online auction business often demands more staff and higher costs as a result. The true benefit, as Sotheby's see it, will be in the general expansion of the market, bringing more business both online and in the salerooms. As Mr Woodhead put it: “We have attracted more new clients in the seven weeks of sothebys.amazon.com than we could have made from live sales.”

Although sothebys.com will concentrate on more traditional art and antiques, and hopes to sell high value art, at least half the lots put up are expected to be valued at under $1000. But they are expecting serious bids for lots over $100,000, and there were several that had been put up for the launch sale by some of the top players among their associate dealers.

With dealers such as, Simon Dickenson, Bernard J. Shapero and Vanderven & Vanderven posting high value lots for sale, it is not just the Sotheby's brand that sothebys.com have to trade on.

There are no clear projections of when the initial $40m investment will be recouped, but sothebys.com expect significant results for single lots within weeks.