Here on The Clark Howard Show, we have something informally known as "Car Call Mondays." Every Monday, Clark's staffers have to ration the car calls because people flood the phone lines after buying suspect used vehicles over the weekend.

With used car purchases, you buy "as is" -- no matter what condition the car is in. The vehicle and all its warts become your problem. If it comes with any warranty, it's usually very limited.

So Clark wants you to do your homework when you're buying used.

First, make sure the vehicle is worth what you're paying. Check Edmunds.com for the true market value so you come up with a feel for the price.

Second, run the vehicle number through CarFax.com to find out if it's a flood vehicle or if it's been in a horrible accident. For the past 15 years, the insurance industry has been able to block a proposed federal database that promised to give instant access to records about known calamity cars. But no more -- look for the database coming soon.

Finally, have the vehicle checked out by a mechanic as a condition of purchase.