I see lots and lots and lots of belts at some auctions. Unfortunately, unless you know exactly what you are looking for and it is there, mostly a dead item to bid on.
Same goes for hydraulic pipes – buy a huge amount for peanuts and only use a couple – then have to offload them or dump the rest. Still a huge saving on the couple you can use, though!
Certainly found it better to buy the I need from a local stockist as they are not an expensive item – apart from timing belts