Some years ago I got a very polite call saying their DYSON data base showed my DYSON was due for a service. As I don't have a DYSON and because of how polite the female was when saying she would remove me from the data base and apologising, I thought no more about it.
Perhaps about 8 months later I got a similar call, this time I was a little more sceptical and asked if she meant "My Hoover" and thanked her as it wasn't sucking properly and arranged for an engineer to call. I had already worked out the way this scam worked: The telesales people phone at random and because about one in three homes do have a DYSON about one in three of those they phone become targets, the other two will usually accept it as a mistake and not report it to telephone preference service - if they're registered.
When the engineer arrived he didn't carry any identity so I wouldn't open the door for him - but after a conversation, through the letter box - I had him shouting too as I pretended to be a little deaf. I eventually agreed that as my Hoover wasn't working properly could he service it on my drive if I passed it through the then partially opened door. (no power supply on the drive remember) he agreed. I had the "Hoover" a genuine decrepid Hoover Junior ready and passed it out for him. He said "We only service Dysons" he then noticed the video camera in my other hand and fled, to a colleague waiting for him in a white van round the corner. I followed.
I do know this scam is definitely sourced from Liverpool and Leeds, and probably many other places. Apparently they use inferior parts and charge much more than what they say is the servicing charge. Apparently many people don't realise they've been scammed until things go wrong.
My only regret about my actions is that I couldn't borrow a rottweiler named DYSON for this scum to try to service.
Incidentally DYSON do not phone people to arrange servicing. So if you get such a call BEWARE!