x3, the last person whos advice you take on a fix should be the seller. i had a very similar problem a while back with a blazer. it wouldnt smog, i trusted the seller when they said that it was the cat and not a big fix. long story short i had to take it to the shop multiple times, it never ended up passing smog and i ended up donating it about 8 months later to get rid of the headache. what you could do however is make a deal with the seller that he gets it fixed, gets it smogged, and saves the receipts, and then just tack on the cost of the fix to the final price as long as its within the range of what he is saying its going to be. trust me you dont wanna deal with the headache of trying to pin point the problem from a long list of possible issues with emisions. thats not even a really screaming deal. either make a deal with him to have him fix it or keep looking. good deals on toyotas come up all the time if youre willing to wait