Darran is a tycoon so not many get to his level
My advice is stick to windows and realise how lucky you are as long as its WFP you do, the reasons being
1/window cleaning is repeat work carpet cleaning is not - this is the biggest factor by far!
2/window cleaning once you have your core customers no further money is needed for marketing whereas with carpet cleaning you constantly paying for marketing for new customers
3/window cleaning business due to its contractual repeat nature as a real worth to the goodwill whereas carpet cleaning is worthless as a business due to the fact that you have no contracts/regular work - just the equipment to operate the business.
4/the equipment required to operate WFP window cleaning is a bar to entry (costing 1000's and van needed too - especially as you need customers too, where'as its possible to carpet clean with a few hundred pounds invested, a car and a deal on facebook or the many discount sites so much easier to enter the trade.
WINDOW CLEANING WINS HANDS DOWN AS A BUSINESS MODEL - WFP THAT IS - traditional NO BUT WFP as real big business potential, your business is actually worth something and no constant investment year after year searching for new clients.
Carpets as a sideline,part time or add on WINS HANDS DOWN - as the hourly rate can be much higher.