I've bought stuff on eBay and on this site. I prefer this site for the "tight" community it is. It focuses more on what's important to me (ie. going lighter).
Several years ago, I bought an aluminum mountain bike frame from a local guy. He and I became friends, rode bikes together, socialized with our wives, and traded more gear with each other. I "sold" him a carbon fiber frame (cheap) and bought a track bike (cheap) from him. I loaned him my tools. He's as close to me now as a brother. It has been an all around good experience.
P.S.—The "family squabbling friction" on this site is minimal by my way of thinking (but fun to "observe" when it occasionally occurs, just like TV Show friction is fun to see. Many of us may have a unique family member we might prefer to sometimes not claim, but the "hand" has been dealt, and has to be dealt with. It keeps life interesting.