We are just going through this now, so probably not much advice yet other than we have asked several companies for quotes. Most have just asked for photos of where it's going and given a price based on that. Only one came out to see it. We are feeling like we will use him if his quote is in an acceptable ball park as he spent ages checking out the electrics in the house, checking underfloor access for running the cable to where we want it etc. Seemed really thorough which gave us confidence he would do it well. Hopefully that will result in us making a good choice!