Well that actually is not true. On my old N73 I bought a battery for €2 that was actually good. It arrived in original package and everything.

What I learned from ebay was before buying ANYTHING from ebay, ask the seller if the battery, memory card.. pretty much anything is in its original packaging. The chinese are geniuses when it comes to copying but most times they omit to provide packaging. So if an item, however cheap it is, arrives in the original packaging, it will most times be original.