I've spent the last month hunting for a used car. In my search for a cheap and reliable cargo mule, I utilized a lot of online tools. Of these CarFAX and AutoCheck were by far the most expensive. To help others make the decision of spending their hard earned dollars for either of these choices, I'm giving a short "lesson learned" I experienced.
#1: They Only Know What's Reported
This is a very important factor to consider. Let's say Joe Smith gets in a car accident with his 370Z. If the police don't show up to take a report, or if Joe and the other person do not report the accident to their insurance company (or didn't have insurance): it won't show up in CarFax or AutoCheck. In the event there's no police report, sometimes
both parties must report it to their insurance companies before it's properly logged. So if Joe doesn't report the accident, but the other guy did, there's still a chance it won't be in CarFax or AutoCheck.
#2: Mom and Pop Repairs Aren't Reported
In order to know what repairs and/or damages happen to a vehicle, CarFAX and AutoCheck need access to mechanic logs across the country. Most brandname dealers and repair shops (i.e. Maaco, Jiffy Lube) grant CarFAX and AutoCheck access to these logs for
quid pro quo kickbacks. However if Joe Smith takes his 370Z for flood damage repair to Bobby & Sons -- and that family owned business still thinks the Internet is a hippie fad -- the work they do and flood report will never be known to CarFAX and AutoCheck. So it will check out clean according to either.
Also note that #1 still applies. Even if Joe Smith takes his 370Z to Bobby Nissan for flood repairs, if the mechanic forgot to hit save or the network was having server issues that day, the report won't get recorded. Thus it won't show up on the auto history. Obviously, personal repairs/upgrades that Joe Smith and his drinking buddies do to the 370Z are never reported either.
#3: CarFAX is Generally More Detailed Than AutoCheck
Several monopoly lawsuits are floating around because of this. Long story short: CarFAX has a better advertising campaign than AutoCheck and therefore possesses vastly more pull with national dealers and repair shops. CarFAX grants these guys more discounts and money to provide CarFAX with exclusive detailed information that AutoCheck isn't allowed. This means a CarFAX report about Joe's 370Z will report -- so long as #1 and #2 above are upheld -- everytime the car gets an oil change, tires rotated, headlight changed, extends the dealer's warranty, etc. Outside of accident or flood damage AutoCheck usually just gets an odometer reading.
This sort of information is useful because it can help the buyer determine if Joe Smith "babied" his 370Z... or in the case of multiple owners, who added the most miles and which state they lived in. Basically it provides insight to driving patterns, which can help with determining vehicle wear and value. Hence the various "monopoly" lawsuits against CarFAX.
#4: It's Possible for AutoCheck to Have a Damage Report CarFAX Doesn't
Because they're heated competators, AutoCheck and CarFAX obviously don't share data. While it was rare, I noticed AutoCheck reporting auction sales of certain cars that CarFAX did not. AutoCheck has exclusive database access of it's own, and this happens for those instances.
#5: Vintage and Exotic Cars are a CarFAX and AutoCheck Weakpoint
Somewhat similar to #2 mentioned above. For cars built in the 1980's and earlier, its often worthless to use CarFAX and AutoCheck, since many vintage owners make personal or specialist repairs. So if you're hunting for that special 240Z, using CarFAX or AutoCheck might be flushing money down the toilet, since it only reports generic DMV records. Most exotic car dealerships are very private with their purchase and mechanic records: they spit on the "chump change" CarFAX or AutoCheck try to offer for access. So looking up that Lamborghini Aventador is probably a lost effort.
Then again, if you have the cash to afford such a car, what does it matter if you spend $50? You're rich.