If you have a mechanic replace something on your car, make sure to ask for your old part back. Additionally, ask that the old part be placed in the box for the new part. This confirms the old part was removed and the new part installed. Unfortunately, there are some unethical mechanics who may try to charge you for work not done correctly, and it could end up costing you double if you have to pay for the repair all over again. Asking for your parts back will help ensure that the mechanic is being held accountable for doing the repair, and will also give you that added peace of mind and confirmation that the part replacement and work were done to your car.