The default case is the that the contestant's trick isn't original to them, and Penn just gives the trick's trade name or its inventor's name, obfuscated a little, and the contestant grins and waves goodbye.

When P&T actually make a guess about an original mechanism, sadly Teller either whispers it or draws it on some paper that they then dispose of in some suitably flashy way. (He's usually right of course!)

They're kind of vague on what the solution is since they don't want to give it away to the audience so they just kind of say a hint. The attempted fooler will generally understand what they are getting at and say if they are correct or not and there are some judges listening who know how it was done as well.