Well, I will just chime in my .02 since something like this happened to me as a seller. I sold my 87 SUnbird turbo convertible on ebay to a kid from New York. I put 4000 miles on the car myself, a lot on the highway, and a lot under boost!
Kid came to pick up the car (I am outside Chicago) and made it exactly 3 blocks! He broke 2 rods and sent them sailing and there was a 30 foot line of oil goin up the street where 1 rod came out the bottom of the pan.
Here's a pic!
http://home.attbi.com/~thorsont/87sunbird06.jpg
Now, I know and you know, this kid took the car out and revved the heck out of it and scattered it. Legally I could have said - "oooh. that sucks. And shut the door." Rather then have that on my conscious, I spent half the money I got for selling the car in getting a shortblock and swapping out the engine. In January, no less. Kid came back to get the car in March, drove all the way back to New York and the only problem was sunburn with the top down. Made me feel better, and I helped out some poor kid who just seems to love those little Sunbird GTs, and who I know couldn't afford to rebuild that engine.
Just some experience I thought I would relay. My point is, that while it looks fishy because this happened so fast after getting the car - these things DO happen, even when the seller may have had no issues with the car.
The 16 year olds driving habits MAY be a little different, and might be the final straw on a rod or crank that is "ready to go"
Either way, I feel for the buyer - borrowing money, 16 years old, now no car. i can hear the fathers' voice now. "Damn kids, always gotta waste money on those hot rods!!! When I was a kid......."