I only buy things from trusted stores. I hardly ever buy anything from Amazon or eBay. There are too many Trusted Vendors you can find by researching an item on ECF to get nearly anything at all E-Cig related from Amazon or eBay. And if you're going to do it, then like Hippieangst said, you really have to watch the Ratings, and read the Customer Reviews. For the Panasonic 18650 IMR 2250 (or Any battery for that matter), I have to recommend Orbtronic, if I can do that here. These Panasonic IMR's are very inexpensive there, about 1/2 what you can pay elsewhere, with FREE S&H, and if you buy 4, you get an additional 10% Off. At least I did last week. And for FREE S&H, the batteries really got to me Very Fast!!! Packaged and surrounded with foam padding in a nice box, with all 4 batteries in a plastic zip bag. Orbtronic is First Class.
I have to agree with Thrasher, too, but I'll go a step further. I think it's Insane to try to save money on something like a Battery. Whether it's Vendor, or Brand, get a Good One, and be Safe about your Vaping. Panasonic is the Gold Standard of Batteries. If they make the size you need, why not get the Best? There's too much garbage coming out of China (and elsewhere) to try to put an cheap, unknown battery in it. At least get the AW brand. I'm not wealthy by any means, but when it comes to my Vape Gear, I go Top Shelf, or I do without. That's just how I roll.