Galerius Maximianvs Coin

Well, the prospective buyer's in Serbia, too. That said, not so far off Bulgaria has been notorious as a source of fake Romain coinage. You might want to take a look at the most recent post in the Fake Ancients sticky thread.

The particular coin in question may well be genuine, but I note that the strike's more or less perfectly centered on an almost too perfectly round flan, which makes me nervous.

There are a lot of really reputable European dealers in ancients on vcoins.com, which might be a safer route than somebody on ebay about whom you really can't tell anything.

I'm not sure then what you're specifically expecting to hear. If you're convinced it's authentic, and that the seller is legit, then by all means go for it. But most folks are going to evaluate a coin in an ebay auction based upon the totality of the circumstances under which it's being offered. I remain of the opinion that the coin itself doesn't look quite right, at least to my eye.