Part of the best offer thing is to HAGGLE. It's like when you go to buy a new car. You offer a RIDICULOUSLY LOW PRICE. And he/she sort of gasps and tries to get you to go up a bit. I don't generally do the best offer because I sell items for women and as a woman, I never liked haggling (until recently). My mother and I did a bang up job when my parents went to purchase a new car. And to be honest, I've done it when I receive an already purchased item, but something is wrong with it, but I still want it. I contact the seller and ask for a bit of a refund. Both times it has worked.
Here's what I think some sellers might be doing--which is what I used to do. Say you have an item up for auction--you're hopin' for a big windfall, but you have a similiar item in your store for a reasonable price--but still, you're thinkin' I could probably get more for this one because it's a color everyone wants. So what to do??? Inflate the similiar item in your store (probably to a ridiculously high price) and check the best offer option. Done it--it works. And in my research, I can see sellers doing this. They're selling a Barbie for say 150.00 with best offer, but that same doll is in auction at 9.99.