I like that way of presenting it, chiph. The main thing is that if someone hasn't done research on how much Best Buy would charge, and you ask for 50 dollars an hour from a friend, it would be easy to offend them. I, for one, had no idea that Best Buy charged $90 an hour. So imagine that I had in my mind that it would cost me $30 an hour to go to Best Buy (what I would have guessed). Instead, my friend does me a favor and tries to refuse payment. When I insist, he quotes me a cost of $150, or $50 an hour, when I thought that I would be spending $90 to go to Best Buy. I think I would be floored. Yes, I would have been misinformed, but I think that it would be easy to have misunderstandings between friends (or just as bad, coworkers,) that way. By saying that you will charge half of what Best Buy charges, although the price will be the same as if you said that 50 an hour was fair, it is more clear that it is a favor. So you are not giving away your time, but you don't give anyone the impression that you are trying to make a killing off of your favor, either.