What I mean is that he is so suspicious of Aes Sedai that as soon as he learned of the Black Ajah, it is easy for him to suspect many of the Aes Sedai for being Black Sisters.

Truthfully, I don't think he is smart enough to figure out who he can trust - in many ways, for example, Verin is far more trustworthy than many of the Lightside Aes Sedai - she played both ends of the game, and her very action of showing him pictures (which we knew had been distributed among the darkfriends for quite some time) could serve multiple purposes.

My main point is that it doesn't really matter what Mat decides to do; the Pattern will start tugging him where he needs to be. All Verin did was pass on her best advice - we, as readers, know that this was one of her last acts on behalf of the Light before her suicide so I think her actual delivery was probably rather wry. I'm not sure if Mat knows women enough to pick up on this, though.