First off, those aren't 2008+ OEM M3 wheels. They look similar, but are not the same. The original 18" E9x M3 wheel is style 219. The real wheel looks like this:
What your friend sold you belong on a <2006 M3, E46 chassis. They appear to be style 135, that have offsets of ET47 and ET50. If that's the case, they probably won't fit. It actually looks like the wheels in your picture are fake/knock offs. Notice how they don't have the slot for the little ///M sticker near the lugs? And notice how the edges of the spokes meet the outer lip very smoothly in the OEM wheel below, but have a little lip/break on your wheels?
Real version of 135-style wheel is attached.