Yeah, VGPC is all over the place for some stuff. It's especially hard to price loose vs. complete for things, and I've seen plenty of auctions where they never even show up in the listing.
I used to use it a bit when I was out and about looking in thifts, but for some reason the mobile version of the site doesn't work on my Blackberry anymore. I think they're pretty close to tiering the data for free and paid and making their own mobile app, which is kind of lame IMHO.