You didn't mention the price.
You won't find legitimate anything on eBay for a fraction of the normal selling price.
This extends to some somewhat-surprising hard goods.
For example, a consumer protection group purchased a quantity of the top-selling Bluetooth headsets from random sellers on eBay.
Half were fakes.
The other half were probably stolen. (My own commentary.)
eBay enables a whole industry in fakes that would not exist without it. Sure, there is a market for fake goods in third-world (and sometimes first-world) flea market, but nothing compared with the world's biggest flea market.
Electronic goods are not handbags. A fake handbag may look good enough to fool others, and last long enough to put in that one special appearance, and thus does the job it was intended to do.
Not so, electronic gear, which may not be a faithful replica inside, and may not perform all the functions of the original, nor as well.
With software, of course, you have the potential loss of registration benefits, which can be significant for a complex product.
I've bought a few inexpensive ($20) software packages on eBay. I'm reasonably convinced that they were legitimate OEM non-U.S. versions, which technically should not be sold in the U.S. but which the manufacturer indulges registration because it would be too much trouble otherwise. (i.e. people buying laptops overseas, etc.)