might not have been a "convenience" issue.

If the mechanic had one or two or more children in day care - there are often outrageous fees for picking the children up late. As in, ten minutes = $25 - 20 minutes= $50, do it a third time and they put your child out. And often there is no viable alternative.

or, perhaps had to pick a child up/deliver child on court ordered visitation in a situation with prior issues.

or perhaps the mechanic had to be on time for community service, one more late and he's out and has to be incarcerated.

And so on, there are a wide variety of possible reasons where the shop have had no viable choice but to close on time.

Your money, you buy your stuff wherever you choose.

However, the shop may have had viable reasons other than "convenience" to not stay open later.