There are often threads on here about oven cleaning and patio cleaning and anything to keep the wolves from the door, especially in January.
Only today I met a guy who just cleans UPVC and clears out gutters. He was doing a door, wiping it down and buffing it with some specialist cleaner. £4 a meter for gutters and £20 quid for the door. I could see the bit he had done was like new and the rest was yellowing. I was thinking.... nice add on, all you have to do is ask.