I think the point Steve was trying to make, was that you need to have a mechanic you trust. If you don't trust him and request a print out, if the mechanic is shady he can make the report say whatever he wanted it to (as ripping you off). And if you planned to use the shady mechanic's print out as proof you'd be fighting a losing battle.
If you feel your mechanic is less than honest find another one who YOU trust, or talk to other MB owners and see who they use (as previously suggested) and get a second opinion.
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