I'd be a bit suspicious of unsolicited offers like this. We've had people knock on the door and allege that ooo, there's a damaged tile or two up there, that they spotted when fixing somebody else's roof along the street -

We had the roof thoroughly retiled a few years ago, and it's under warranty, and anybody else messing with it voids the warranty.

Also there was some doubt whether operations like this are entirely on the up and up and only about ripping people off with possibly spurious tile-fixing....