Ebay and COMC here. Check out my S&T thread (shameless plug).
One thing I will say is if EVER in doubt, ask, ask, and ask more questions. When I jumped into vintage I made the mistake of not scrutinizing pictures and asking enough questions only to receive "NRMT" cards with creases. After some initial lessons it's been pretty smooth sailing. My advice is if it's anything of substantial value to ask questions, ask for additional pics, etc before buying. If the seller won't oblige then move on to the next one.
Good luck!