Buy a cheap engine scanner. They are easy to use. You follow the directions and read out the code which is usually decided in the instructions that came with the item. Harbor Freight often has then for under $50. It is well worth it to see what the check engine light is telling you. I had an older Chevy pickup that used to get the check engine light after every big storm and showed as a minor pollution system leak - I think the rapid change in barometer pressure was setting it off. I would reset the indication with the tester per its instructions. Pay wife’s older PT Cruiser occasionally gets that indication and when checked it actually shows no fault. I restart the car’s computer by disconnecting one terminal of the car battery (with car off) for a couple of minutes and then reconnect and that fixes that. By the way I am an electronic engineer. Even if you cannot fix the problem knowing the trouble code and looking it up online will get you an idea of if it’s a serious problem or not. That way if the mechanic tries to screw you over, you know to take you car elsewhere. And by the way, the seller should make good on the problem given the timing.

Lemon laws must not exist where you live