I buy a fair bit at collective machinery sales and farm sales, motorbikes come up, though I have yet to buy one, but just like ebay, there are all manner of people selling, from crooks who are palming off totally shoddy junk - often tarted up to look better than it is, to genuine good stuff in very reasonable order. As with ebay, you look as best you can at the goods, and decide on a price you won't go past that takes into account the risks. Some auctions do offer some form of garuntee that stuff is working if sold as such ( but for how long!) Good point about watching out for vat and buyers premiums.
Prices can vary even more wildly than ebay, I have seen old wrecks get three figure bids, and what look like genuine barn find mopeds, complete with keys in the ignition and a layer of dust for under £5. I did visit one proper dedicated motorbike auction, but seemed to get high bids for often dammaged bikes, and you were charged entry which seemed a bit like money for old rope. Trouble with these things is often there are traders who'll mop up any bargins and try their luck on ebay. Seen a fair few vehicles double their money from conventional auction to ebay, but the traders will happily run you up to close to the ebay value if they have space in the van.
