From the mechanic's perspective, this can be frustrating especially if they are sure they didn't scratch your bike. BUT, this is an awesome opportunity for the shop to retain or gain a very loyal customer. It's an opportunity for a "WOW!" moment where they can go above and beyond to make you happy. It's nice to have decent customer service, but the one time they give excellent customer service is the time they will keep that customer coming back over and over again. You don't have that many chances to really wow somebody, so they should have taken the advantage to do that.

My advice? Pick another bike shop, and allow them the chance to really impress you.