We have found keeping paper trails(Records of proposed and completed work) of all Work done on jobs either Service calls or Contract work will save you in the long run.

We had a service call with a new client asking us to fix an install from another company he was given a quote of the work to be done, after everything was completed as proposed, he refused to pay the balance stating we never fixed something in another room. the original work never involved any other rooms other than the main system and he was reminded to look at the original paperwork. He had mentioned to one of the installers that the other room needed work and was told it could be looked at if time permitted.

Well as noted on the work order, it was looked at and client was informed the tv in the room did have an issue and was advised to have a television service company take a look at it, and said he would call one.

so again he was reminded it was looked ay and he was advised to call a tv repair guy to look at it...

he then relized he was told about the tv and needed to call tv repair guy to fix.

Our office gal would have never known the bedroom tv was looked at as the tech was out of the office and the work performed was all tracked on the work order.
So I guess this is a reminder to track all work perfomed and conversations with people, this would go for all aspects of the job....sending components in for repair and so on