Keep offers of selling out of this thread -- please.
Personally, I wouldn't waste the money on a mated pair -- just "make" a pair and let natures take its course. However, if you do purchase a mated pair, I would ask for a video of them spawning, or at least a picture. Also, moving to your tank will disrupt their spawning and it could take a while for them to spawn again.
Edit, I have a mated pair of WC percs, but with 2 tank moves in the last 9 months they haven't re-started, so as you can see it can take a while.