Could he not sell it on again or did he pay too much in the first place? What forces people to give up? To much graft, not enough work? or money too low?
They guy I sold a little bit of work onto just dumped that work, because I had the customers wanting me back. I'm not sure if he sold on the other stuff he'd recently bought; but I don't think he did.
I think this guy had read too many posts of high earnings here, thought he was a bright hard-working guy; but then found it was far tougher than he thought. He went back to his old job with was Head Gardener of a local five star hotel.
I think it was a combination of high expectations and a lack of experience, when he needed it the most (at the beginning) stuffed him.
I'd keep your present job and build a small part-time round, around your present occupation.
You may find out, like many others do, that window cleaning is not for you.
I hope I'm not being overly negative; I'm not; but I'd hate you to have a rosy idea of what window cleaning is like from the posts you read here.