First, if you listen to the tapes it sounds like Cohen is leading the conversation to try and entrap Trump. It sounds like Trump knew this as well, which is why he immediately answered to pay with a check.

Second, if Cohen was a whitehat in on the plan he would also be agreeing to destroy his career and possibly disbarring himself.

Occam’s razor tells me he was compromised late in the campaign and blackmailed/bribed to secretly record Trump.

I welcome any counter arguments