[what?]

yeah, you won't get charged if you have a fault that is still something gone wrong on the virgin equipment, but if he were to get a technician out, and the result was that one of the cables fitted by a cus was at fault, he would b liable for a £75 charge.
not all tech would apply this charge but there is some who would, so just pointing out that he has to be careful what he does with the set up and be aware of posssible charges.

obv he has said he is qualified so doubt it would b a problem, but just letting him know.