I've never sold a car "for a friend" but I have sold quite a few parts for friends who, as said above, don't do the internet/forum thing. I'll normally say that in an ad just because some questions will take longer to answer because I have to ask the friend. Without saying it, it could appear as flaky. Most buyers are understandable, but every so often I'll get someone who thinks they're Sherlock Holmes and just uncovered a million dollar scam ring.