Carfax tends to get a bit "militant" with their customers, especially if you are screening multiple cars. They think you are running cars for other people, and start harassing you in various ways to inquire why you are running so many reports. I found that rather annoying back in the old days when I used Carfax to screen potential purchases on EBay - and I stopped using them when I received a "rather hot" message from their representative that had reviewed my account usage. I paid for an UNLIMITED account and I expected to be able to use it in an UNLIMITED manner.
(We're talking about a max of 20 reports or so in the 30-day subscription period back then....)
Since then I have always advocated and used AUTOCHECK.
EBay has started to include Autocheck reports on almost all modern vehicles listed (since the 1981 VIN standardization) and if you want to get a good idea of what is contained in the reports, look over there.
Autocheck is great for -screening- cars out of contention for purchase. You will see things like "accident" or "salvage title" that might knock such cars off your potential purchase list. But do not actually buy a car long-distance based only on a clean report.
My personal method is to use Autocheck for screening out undesireables, and then go take a in-person look and test drive of the ones with good reports. In the past I have bid and won cars on EBay, but informed the user that I would need to inspect the car in person (and drive it) before I would pay. The honest seller who has described the car accurately will have no problem with that.
Ken300D