Just change the word purchase to swap and BAM! That should take care of legality all around. If person A has a clone that they value at $200.00 and they only find person B with $20.00 clones/strains, well, that's that. Try again another day or network with more patients to find somebody with a comparable swap. Maybe not the strongest suggestion, but simple.
I think there is a distinct difference between cash croppers and growers who grow for the love of the plant. To one, it's likely a job, a means to an end, not really about the patients. To the other, words like profit, purchase, legal, aren't really in the lexicon. Of course there is a grey area but I don't really see any problems obtaining great genetics here, but it depends on who you know and what you do.
I continue to believe that MMC's won't put their best gear on the clone shelf, and I think that's the rule, although there are some exceptions. Your problem might be obtaining genetics via MMCs or cash croppers. I think there is probably more competition within cash cropper circles than there is with growers. Different goals for different situations.
Have you been to any seed company drops or are you just posting about clones?