Wow, I had a similar experience. I left my truck (beater) at the shop for like a week and the dumb mechanic left it inside everynight with the windows down. I had candy in the back and needless to say these were rats. Lots of rats had a feast and left lots of poop and urine everywhere.
The mechanic was unaffected by my complaint. So I had the truck completely detailed, steam cleaned and sanitized. And just sold truck.