I'm looking to buy these M6 rims, and the guy says these are OEM..
What do you all think?
And how do I know if they're OEM or replicas?

You need to check the inner spokes of the wheel for the BMW stamp. This is the only real way to tell if they are OEM.

From the pictures though, I would say they are OEM. I am basing my opinion on the concavity.

Should say BBS Germany on the inside.

as stated above, ask for pics of the back of the wheels..also ask if the seller as the original bmw center caps, unless you like those beyern center caps...

Not sure about them being oem as the center caps seem to be the Beyern wheel logo. Then again Beyern wheels doesn't make M6 replica wheels?

Take a look at their logo on their site http://www.beyernwheels.com/index.php again just odd!

They look like Style 167's which are an M6 wheel.
Check them out here:
http://decrass.ru/bmw/wheels/

Click on the ? above the pick and it gives size data and OEM part numbers.

Another clue: It appears that OEM wheels have a small "///M" emblem in the space between lug holes, and the pic you displayed does not appear to have it, though I cannot be sure due to the size of your pics.

I have OEM 167's the best way to tell from the replica is the "C" curve you see on the OEM's. I have marked it on the wheel. If it is "L" it is replica.