Sam was still reeling from the appearance of Jason, and the woman's quick dispatching of the masked baddie, so it took him a moment to realize they'd arrived at their intended destination. Sure, he might possibly trust a human more, but if he'd known it was a wizard they were going to see, he might have been a little skeptical. He might have been a little suspicious that she was making things up about Dean trusting the guy, too, because Dean felt even more animosity toward witches than Sam did. If such a thing were possible after the double-whammy that was Ruby.
"Dean and I don't always think alike." After all, Dean would never have thought about saying yes to Lucifer and throwing himself into the crack of doom.