Its gotta be one of two things:
an XP chip
He is wrong about the speed.
If the seller is right about the speed it could be a couple of different things still though:
XP chips have a few different cores-
Palomino was first and the 1700 Pallys were not great chips for ocing
Thoroughbred has a few sub categories, but either way is better than a Pally core. The TBred B cores are preferred.
Unless the price on this chip is absolutely fantastic- like less than $10 USD it sounds pretty risky to me.
TBred B 1700 are still available and only about $47 USD right now.
That chip sounds risky and if the seller knows that little about it, I think there is a decent chance that the chip is dead....or will be by the time it gets to you.