Well, as the saying goes, the value of anything is what the market is prepared to pay at the moment. So, I sometimes wonder whether my beautiful railroad grade watches would fetch what I paid for them. On the other hand, any watch with "Seamaster" on the dial appears to go for silly money.
As for sniping, I must confess to having done a lot of it in my time - and won a lot of eBay auctions by doing so! If you really want something, and are prepared to pay for it, then sniping is the only way to do it. Putting a maximum amount on a standard eBay bid reveals your hand as other people bid, whereas sniping reveals nothing until the last 5 seconds. In both cases, however, you have to be prepared to fix a maximum.
Ebay auctions are not as much fun as online saleroom auctions, where you really have to get a grip on yourself and stop bidding when you mean to! Even better is being in the room itself.