How can I tell the rims (rs6 18") are OEM or Rep.?
Any tips? does OEM rims have audi logo on the back or something?

Thank you very much

on the RS6 in the US, you should be able to tell on the inside of the wheel if they are replicas. On the inside of the wheel (at least the ones from Hartmann and Achtuning), the replica wheels are stamped something like "Replacement part - not OEM" They'll also be stamped "Italy". I'm pretty sure OEM will have the rings or VW stamped on the inside, and will probably have the part number stamped in there as well.

the OEM wheels have the Audi logo. part number, say Germany JWL and size 18 8.5. I've got a photo of the casting if you need it.