Not done any of this with a six but the way it used to work with the 5 is £59.99 for screen then £169 if there was an actual problem with the phone. If they fixed it for less u got a refund of the diff. If it was anymore serious ur £169 got u a brand new phone with a used processor!
I got mine wet and I knew someone in a store, (they've left now) but I paid £59.99 for screen and got a new refurb phone
The 5 is more money than the 6 for a new screen