YKA
Pre-takeoff checklist
Never found anything left in my planes, but opened the hood of my GMC pickup for a look, before driving away from the dealership after a service, and found a 3/8" drive ratchet, and deep socket on it. I always look over my vehicles before I leave a dealership after they do any work, because I don't trust them. But after find that, I looked extra close that day. Then I walked inside, showed the service writer what I had found. Let her know how annoyed I was about it. Then i went to the reception desk, and asked to speak with the general manager. Voiced my displeasure to him as well. He returned the money I had just spent on my truck, and apologized. Never trust any mechanic, always double check their work.