I would think for friendly sets you would want to play better players, what makes someone a champion is an open debate. Don't listen to this advice, sbc is obviously not correct on this. That is not to say that the game can't be adjusted after the first set if the match is lopsided. But I think sbc may be thinking with the ego or fear on this one. Pros and champion is again an open debate.
I think I could learn much from a pro if their friendly enough to give up some information. Most I have met are willing to give up a nugget here and there. I got a chance to play Mika Immomen in New York City a while back. I asked him to play 20/rack 9 ball for about hour before he had to leave but then for him to give me some advice after we played. Best 60 bucks I ever spent gambling with someone I had no chance of beating. I have found most payers, once they beat you they want to give you advice. My ears are always open.