Someone whose name would be familiar to everyone had a bad experience with MM. It was a mistake a child wouldn't make, and happened just prior to an event.
Sorry, I can't give more details other than:
1. give them exact instructions in very clear language: operations, parts to be used, measurements, prices
2. make sure they acknowledge this
3. when you get it back, assume nothing, examine everything.

Maybe they're better now than they were, but that's what I would do.