I've selected canvassing, but that oversimplifies it.
The canvassing would be carried out by me after 3.30PM or at the weekend and the £1k used to pay me (partly) in lieu of any windows I don't clean to due to doing that canvassing.
I reckon that I know better than anyone exactly what I want, so I would be the one to do it.
If I reckon £25 an hour for canvassing, that £1k would pay me for 40 hours in chunks of 2-5 hours. I would reckon on picking up at least one customer per hour at an average of about £18. 40 x £18 = £720 and 8 times a year would mean £5,760 p.a. Any dropping out would likely be balanced by walk ups.