You decide on a minimum price and list it, in auction format on Ebay, then hope for the best. If too high, it won't sell. If too low, chances are good a couple of potential buyers will hop on it. And all it takes is two serious buyers.

I have a Legnano embossed headset that I do not know the value of. I just might list it but the price will start at $100.00 and interested buyers, if any, can decide for themselves on final value...