Can auto technicans take advantage of you, especially if you're a woman?

I have a 1998 Chevy Lumina, my car would not start. Luckily, this all happened in my driveway and not on the highway! I called AAA last night and he tested my battery and alternator, both were in poor condition (the alternator tested in the yellow, about a 12). Before this happened, I left the car running for 10 minutes to warm up (I live in MN), but 3 hours before, my car was running normal. I explained to a family member about what happened and he said, quote, “that doesn’t make any sense”. I moved to a metropolitan area where I do not know anybody personally who can even help me to repair my car. Also, too, I’m worried I was taken advantage of by the local auto technician. Could there be another underlying issue that the technician didn’t even want to take the time to diagnose, such as maybe tightening the alternator belt or just charging the battery altogether? Before this happened, none of my indicator lights came on, such as the battery light or service engine light. Thanks for the help!