I'd start by looking at the feed back for that battery. If a lot of buyers are giving positive feedback then $10 is a good deal, or at least a good gamble.
One thing about modern electronics is that there's only a handful of manufactures for many of the components that go into them. Things like LCD's, processors. LiOn batteries, RAM, etc... They all come out of the same handful of factories in Asia. The manufactures often produce the same or almost the same components for competing products. So I'd say it doesn't matter much where you get them (as long as they're new). The seller is probably getting them wholesale and only getting 100% markup rather then the usual 400%+
my $.02