When i try to trade with Mick or Ralph, they'll say "Have a look" or whatever, then the trading interface won't open, it just brings me back to the dialogue.
So far i've only had this problem with these two. Repair works fine with them
I have all the DLCs but i'm pretty sure i've been having this problem since before the DLCs.

Edit: Just went searching through the forums, same problem as this http://www.gamesas.com/index.php?/topic/1192101-very-odd-mick-ralphs-glitch/page__p__17715613__hl__mick__fromsearch__1#entry17715613