When it's running, is the reverse button stuck pushed in? If not, what happens when you push it?
ETA: For that matter, when you turn the stitch length dial, does the reverse lever move in and out?
Absolutely the worst situation I had with a machine running backwards was the timing of the dogs was off. The lady'd managed to throw it 180 degrees, and not affect the hook timing, which shocked the heck out of me. I stared at that machine for a week before I was willing to take it on. Took me 10 minutes to fix it, once I got in and did it. LOL! That's the issue to troubleshoot last though.
I agree, especially "in this economy" I don't understand why people would turn away business.