To avoid any unnecessary unpleasantries when leaving your car with a dealer, ask for the receptionist to do a tour of your car with you to note any damage present at the time of inspection. You both then will sign a form noting any current damage. This way they will note down (in front of you) any damage present. On collection of your car ask again for a post repair inspection. If you and the receptionist note any additional damage you will know where this damage has occurred. Simple init! Always be polite but firm, no one likes a smart @rse.
Try it - it does work!
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