Why Are Dell Laptop Batteries So Cheap on eBay? (quality, money)

[VGravitas]

If you bought a Dell laptop battery directly from Dell, it would cost you over a $100.

Yet, I see many on eBay that appear to be brand new and are less than $20:
dell inspiron battery | eBay


Why is it much cheaper on eBay? And is it likely that the quality of the product will be good?
What should I look for/look at in order to determine if I'm likely getting a solid product?

[bUU]

This is not a genuine Dell battery. I've got a replacement Dell Inspiron battery right here, which I bought in a similar, vain attempt to save money. It was money foolishly spent.

[yowps3]

Fake battery..

I'm starting to use eBay less and less because of them reasons..