IMHO: Retail value is not established on one auction. Track auctions of the same item for several weeks or months, and you will be pretty close. Some auctions go for more (sometimes a lot more), some go for less (sometimes a lot less). I always bid on the low side, so any second chance offer is a deal (well below retail). In my case, its a big risk to not accept the second chance offer. Since I bid well below retail, odds are, if the item is relisted, it will go higher.

Now if it is a really rare item, that you don't see very often on ebay, you have the second problem of timing. Are you going to see another one for sale, and if so, how long will you have to wait? I'm pretty patient, so that is not as big a factor.