What can I expect of mechanic now? Car caput

I stupidly bought a 93 Colt Vista wagon about 3 weeks ago. Drove it 120 miles first day; second day it wouldn’t start. Had it towed to shop. They said to take it to an “e” shop. Took it to recmd. shop: asked them to diagnose prob and generally check the car over. Said I needed a computer. Found a computer for 175, they installed it; also replaced battery, did tune up, changed oil; serviced transmission…said car was good to go. I then drove the car 240 miles: and this morning it won’t shift into reverse and engine sounds LOUSY. Do I have a right to expect more from the mechanic or am I stuck with a DUD? What can I ask of mechanic now?

Take the car back and see what is going on.

Maybe a bad mechanic experience but the more realistic thing here is that you purchased a 16 year car. Expect anything and everything to go wrong.

If you decide to dump this car before purchasing your next potential to a mechanic and pay for a checkover.