if they are in fact OEM 2 piece AMG rims made by BBS then they are the real thing. Originally they were pretty pricey. I know my 18" 2 piece were a $5,000 option (in 1998!) but can't speak for the 17". I would guess new they were around $3k?
But used? The sad state is that no matter how rare they are, not many people like to jazz up an older MB, so not much. If you're lucky, you'll get $1000 out of them.