(Quick story) I remember one time my sister had her car repaired when she was out of town.
She was driving and her check engine light came on. She called me in a panic. I told her to take it to a chain store and hope for the best but to ask for the old parts back.
The shop said the vehicle needed an o2 sensor and my sister confirmed the light was out and received the old part.
When she got back in town I asked to see her old part, it was not an o2 sensor but an egr valve off of a large diesel engine. Definitely not from her little economy car gas engine.
When I looked under her car the old original o2 sensor was still in the exhaust stream.
To make a long story short the shop just cleared the check engine light and let her go after confirming with her she was heading back to her home state.
Two things to learn from this. One if you have out of state tags tell the shop you just moved to the state your in and have not changed your tags yet.
The shop knows that if you are a transient customer that they will never see you again and can give you the royal screw over with no problems.
The second lesson is if you ask for the old parts back know what the part looks like.
Have the shop show you the old part on the car before they remove it so you can confirm it is the part quoted in the repair estimate.
Learning some basic automotive skills will make you feel more confident about going in for auto service. The service writer or service manager will instantly recognize this confidence.
A consumer that understands the vehicle and how the auto service business works is usually passed over when it comes time to apply the rip offs and scams.