On Lastminute.com (www.lastminute.com) which offers a range of holidays, gift s and tickets at the last minute, consumers will sometimes pay a premium to get their hands on a rare concert ticket. At other times they can pick up goods chea ply - such as hotel rooms - because the hotels would rather fill beds than leave them empty.

Perhaps the most significant development has been the emergence of onli ne auctions, a sort of high-tech electronic flea market. eBay (www.ebay. com), f ounded in the US, has become the leading online auction house and now has offsho ots in Europe. With more than 4.5m listings (details of how many items have been up for auction) and 10m registered users, eBay is a good place to find the thin gs you want or to sell the items you have. www.ebay. co.uk offers a site tailore d to the needs of British traders and collectors combined with the largest and m ost advanced online trading community in the world.

It was originally cre ated because the founder's wife wanted to be able to find and trade Pez dispense rs (yes, the plastic containers which dispense Pez sweets). On the UK site, item s such as Wonder Woman Pez, Flintstones and Batman Pez are available.

The re are hundreds of items, which can be paid for with credit cards, banker's draf ts or personal cheques. You can bid on everything from a Tetley's huntsman sign, to vintage sewing items, to the "Kate Winslet Titanic photo nude painting" from the site's risque section.

eBay has emerged as one of the most highly ra ted internet stocks. Unlike some of the e-tailing models it looks less vulnerabl e to the threat of offline competitors moving online - such as airlines selling their own tickets direct to the consumer, bypassing internet travel agencies. eB ay looks sustainable because it has created a model that would be impossible to replicate in the offline world, thanks to the ability of the internet to aggrega te limitless numbers of buyers and sellers.

The company also gains compet itive advantage from having customers, high-margin revenues and a low cost base. It bears none of the shipping or inventory risk, nor does it need to have a vas t fulfilment operation to ensure the goods are delivered. According to Salomon S mith Barney, eBay accounted for "$2.8bn, or 13 per cent, of the $22.3bn in total value of consumer transactions (for consumer online marketplaces)." The report added that eBay was the "largest, fastest-growing and most profitable consumer c ommerce site on the internet."

Not surprisingly, eBay has spawned a numbe r of copycat rivals in Europe. Its dominance has already provoked a wave of cons olidation as smaller European start-ups merge to create a convincing rival. QXL. com (www.qxl.com), the UK-based auction company, has been leading this consolida tion, buying rivals in the rest of Europe. Even so, such is the strength of eBay that QXL's shares have had a volatile time on the stock market. Despite this, t he company is likely to continue gaining custom and, with its focus on local con tent and goods, offers a solid counterpart to eBay.

QXL Direct is where Q XL buys goods itself and auctions them off. At QXL Merchant Partners it joins fo rces with manufacturers and retailers to help offload stock such as British Midl and air tickets, fridges, holidays and computer gadgets. QXL has won the right t o auction the whole of Wembley stadium - tap fittings, plastic seating and the t urf.

The site also has consumer-to-consumer auctions. Like most auction s ites, it provides an online pseudonym enabling buyers to bid for goods anonymous ly. Registration is free and so is offering items for sale, but QXL has a slidin g commission structure on sales.

It charges 5 per cent on items between £ 0-£15, 2.5 per cent for those priced £15-£600, and 1.25 per cent for items of £6 00 and above. Vendors can track auctions online, be e-mailed or contacted by Wap phone if a bid is successful.

Hugh Scully, the former presenter of the B BC's Antiques Roadshow, has also been brought into the QXL fold. For a £12 fee, beneficiaries of family heirlooms can have them valued. They e-mail or post a ph otograph of the item and fill in a form with indications of where to look for ma nufacturers' signatures. Enquirers are then e-mailed a valuation.

As with many of the auction sites, however, the excitement of bidding can overtake a ra tional analysis of what items are really worth. Often, consumers end up paying m ore than they should, and it is hard to get clarity about whether you have got a real bargain. Many products can lie forlorn on the site for days with no intere sted browsers and never hit their reserve price. Also, there are some unique sec urity issues about buying from strangers in auctions over the internet.

O ther new pricing models have emerged. This summer, www.priceline. com announced plans to enter the European market. The business model has proved immensely popu lar in the US. William Shatner - better known as Star Trek's Captain Kirk - has helped customers boldly experiment with new ways of shopping online.

The site has helped to shake up the way people shop for airline tickets, mortgages, hotels and other goods. Instead of just comparing prices between sites, consumer s can take a more active role and name the price which they are willing to pay, and support this with credit card details. Sellers get the benefit of selling th eir goods at different prices without having to dilute their brand: the seller t ypically remains anonymous during the bidding process. In eff ect, customers are trading brand preference for price. Even so, a majority of offers posted by con sumers are not met because Priceline can't find a willing seller.

Ybag (w ww.ybag.com) is a personalised buyer-driven shopping service. The basic idea is that rather than having one item and a number of buyers, you have one buyer and a number of sellers. It works like a reverse auction, where retailers compete fo r your business, helping to drive down the price. So consumers, not sellers, hav e the power.

Those who want to, then make a request for goods, such as a television or a computer. Ybag sends this request anonymously to its suppliers. Retailers respond with their best offers. If interested, you can be connected fo r free to the suppliers. You are not obliged to make a purchase.

The inte rnet can also help reduce prices by bringing together customers who want to buy a particular product, in order to get cheaper deals. In some ways it matches the buying power of large high street stores. www.letsbuyit.com, set up in 1999 in Sweden, aims to do exactly that. It has become one of the best-known examples of aggregative shopping. The price drops as more customers register to buy.

Although shopping in this way can be novel, and exciting to watch as the price drops, there are a few downsides. The goods are not always cheaper than speciali st sites. Customers have to wait for weeks before they can get their purchases. Letsbuyit will often not approach a manufacturer until it has enough customers s igned up, creating some uncertainty about what the final price will be. For exam ple, over Christmas it failed to deliver some of its bargain-basement £7 Christm as trees on time. It reimbursed all those who had bought a tree, but that rather defeated the point.