If the work done on car doesn't fix the problem, are you still liable for the cost?

I put my car in the shop to be fixed for smog. The car is old and I was considering selling it for parts, but this guy, who has worked on my friend's cars and has a good rep, thought he could fix it and for less than the other quote I had. Now, the wiring harness he installed hasn't fixed the issue, in fact, he said the emissions are WORSE now, and that it may be the catalytic converter after all ( he had dismissed that possibility earlier, bc it's a fairly new converter, and the wiring harness was so old, he was certain it was that due to other small problems the car had). If so, I'll be back to selling the car for parts and needing a new one. So, if he did the work, but didn't fix the problem, and I still have to sell my car, do I have to pay for the work he did do? I don't want to screw him over, but on the other hand, I would have had a new car by now, and the money I'm spending to "fix" the car, would have been put toward tge new car. Now, I'll be in the hole.