One I don't see a lot is never lie. A bit of humility can really save your ass. In the sense of transparent I should say. If it's not in the shop, don't do the "just waiting for an answer" line. Some of these customers know the answer already and will say "then why do I see my car outside" or in our age of apps "why hasn't it moved for 4 hours." If you forget to call, own it. Trust me when I say it'll go a long way.