I don't think this is correct, but just to get the ball rolling I'll go with the GP salesman:
For those in a hurry (quick way to get GP rather than having to earn it)
Please pay a visit (obvious enough)
But if you don't see (The italics worried me, though you can't see him when he isn't there, quite rare for someone to disappear in FFVII)
What you want (Him/GP)
Then go away and
Come back later (He spawns randomly (I think), so if you leave and come back he eventually will turn up)
Oh, and thanks... I think... I was aware of the riddle you're talking about, but didn't follow it so I don't know what happened with it