Always check the engine bay of your automobile when you have work done. You never know what treasures you may find. This was left by some in mine. It’s magnetic, so it was stuck to the side of engine bay tucked away we’re you could barely see if. 😂😂😂 
Discussion
I still haven't found my 10mm socket.
Bummer for that mechanic. Those are like $150 🤣
I would return it. Technicians have to buy their own tools amd most spend 70-100k over their career. Not cool to keep a lost tool, especially when you know where it belongs.