I remember the good old days when you go in a sub's house and see an old t.v. with the tuner knob missing and there would be a pair of pliers laying there to change the channels. You bet your ass that they would try to get one over on you for a new T.V. Move furniture? Hell no, learned the hard way there too.. As an in-house service tech I've had to verify that some scum was lying about a contractor damaging the set, pisses 'em off when I bring in a test t.v. and with my knowledge of electronics, spoil their case!
I won't touch a cable modem install unless the sub turns on the 'pooter first to verify that it works before I start, and then I show them where the connections go and after getting the thing working having them re-boot again to verify all is well. Remember the 3% rule...Only 3% of the people you deal with are really Assholes but you deal with them 97% of the time!