Postcount is over exaggerated to say the least. But then again (for the older crowds) Credit Score is merely a number too but it can bless you or fuck you to say the least lol. I say use good judgment; if they have reputable vouches and a good set up of good trades, and they PM you, and all that fancy stuff, then it weighs more on the trusting side. But, at the SAME time, a higher post count for these kinds of people is viable.
For example, you take a guy with 5 vouches that has 20 posts. Sorta fishy wouldnt you say?? (Especially if their vouchers have no PC as well). BUT, say he had 300 or more and 5 vouches... It looks, LOOKS as I said, more viable. Just my opinion.
But your best fallback is your good judgment. Don't wanna trade?? Then don't do it. But to say it DOESN'T MATTER is a little out in left field. In essence it does. Just not to the degree some of you people put it to.