There is always the chance the garage needed a bit more work that week and you looked like the person to up his wages, just a thought. I bought an e class e320 estate and had a so called merc specialist check it over for me when i bought it. I told him i had just bought it and wanted everything checked even an oil change. when i went back he told me the turbo inlet port motor (i think thats what it was) was about to give out a know fault from an oil rubber on the turbo never fitting properly. he said take out this warranty with me leave it a couple of weeks and i can claim on it and fix it for you, the warranty was about £300. the price to get it fixed was about £650 as its deep in the engine. I went mad at the dealer i had just bought it from he said what lights have you got on the dash, I reply none i told him what happened and he said rightly, he put it 'he's pulling your pants down and .....'' I never had it done and never went there again, i had that car 8 years and it always ran perfect i serviced it myself after that except 1 year i started to change the oil and taking off the floorpan came over all dizzy and thought you know what i am too old for all this now get someone else to do it for me, i took it to another so called merc specialist telling him he will get all my work from now on, i gave him the merc oil and filter and pan to put back on, he charge me £110 this was about 3 years ago for the privilage of doing it even though i had given him the stuff, so the next year i feel ok i will do it myself and, when i took the filter out he put a crap cheap filter in not the merc one i gave him so i have no doubt if he nicked my merc filter he certainly didn't put my merc oil in. I have found someone now in the last two years i can trust and i know there is some on here that are excellent and come highly recommended, but this is just a warning that there are some snakes out there.