MAYBE THEY RIPPED ME OFF!!!
Long story but could save you in the end - I needed a specific tire replaces and they replaced the wrong one on purpose without consulting me the customer - I found out the next day when I woke up to a flat tire again and saw that a different tire than requested was replaced. Their explanation was that they believed the tire they changed was in greater need of replacement - even though we looked at all four tires together and agreed that only the tire I requested needed changed.
To prove their point they pulled out an old tire that looked like it was machined down to the steel in a very isolated 3" area that looked nothing like the ware on the rest of the tire.
My fault - should have checked the work immediately, but instead, assumed that their smiling faces and well wishes while I paid them meant all was done according to plan.
So did they mistakenly change the wrong tire and then grind it down to the metal to cover their rear ends? I think so, but maybe not... What they did do was leave enough room in my mind to speculate and feel responsible enough to warn others of their poor practice.