Carfax doesn't always show everything, that's why the buyer has to use their own discretion and ask everything they should, as well as feel out the seller. As for dealers, I don't usually bother with them because of the fact that they don't know the car as well as the owner would, etc.
Never heard of Autocheck.
after using both, Im gonna have to vote for Autocheck, they include the info for Auctions and stuff, and have consistently more records than Carfax..
plus, its 45$ for unlimited checks for a month, vs. carfax 45$ for 4 checks period...
Ive already looked at 4 cars and havent picked one yet, I would have been putting down another 45$ if I didnt switch to AutoCheck...
Plus, Autocheck is done by Experian, which is a credit agency.