2000 Mercury Cougar What else could go wrong?

My daughter is looking at a 2000 Mercury Cougar. It's a four cylinder with 102,000 on it. The seller (a used car dealer) wants $2,500 for it. The car is in great shape, and it should fetch twice that much, according to Kelly BB. The seller says that the catalytic converter needs to be replaced. Actually, I'm told that the Cougar has two of them. We have recieved and estimate to replace the converters for about $700. I'm concerned that there may be more wrong with the car, even though the Carfax VIN checks out fine. Could a clogged cat converter cause damage to the engine? If so, how likely is that to have happened? We will be grateful for your advice. Joe Shinnick