I used to say auctions but now am thinking BIN. A lot of buyers sort for auctions only and if you have patience to search the BINs you can find some winners. You can also work some deals on the BINs if they've been around for awhile.
Ebay is changing to a BIN world because beginning sellers or ones with less than 300 feedback (me included) are sometimes afraid that their items won't get enough exposure to get full dollar. Buyers seem to look for their favorite sellers with 20,000 feedback and the non-pros listings will sometimes get buried in all of those listings.
So, the beginning sellers putting their items up either way high or reasonable or at a bargain. When those items go up as BIN and you search at the right time, you can find some really good deals on some more rare items. Like Leon's blank back. You just have to be a quick draw from TX.
My experience is that the volume sellers will use auction and that the mom & pop and hobby sellers use BIN (with some exceptions). I like to see what the hobby sellers have because typically it might be something a little out of the ordinary.