In the sixties and early seventies, vintage car prices were ramped up in auctions by sellers buying back in through a third party and putting back in auction again a few weeks or months later. That is very easy to do on eBay. Let's say you have two bicycles of the same make. They have to be something desirable and you would expect perhaps five or six hundred dollars for each. You put one on eBay with a reserve of 800 dollars. It 'sells' for 900. After a few weeks, you put up the other bike and it 'sells' for 1200 dollars. You now have two bicycles for which a value has been established. Don't put them back on eBay as someone on this list will comment. Put them into one of the occasional conventional bike auctions with a reserve of a thousand on each. There will be punters there who know what the bikes are worth because they follow eBay. You do not have to have other than a passing interest in cycles, and you do not need to restrict your trading to cycles. With a little practice, you can become a greedy trader in almost anything.
Stuart Tallack in West Sussex