Biggest problem is kinda like many other small businesses, you end up being on call 24/7 (okay, really more like 18/7 since nobody is cleaning at 3 am.) and unable to take vacation, or even reliable weekend trips out of town.

Staffing is also a continual problem. Even if you pay significantly above market, cleaning isn't a very in-demand job, so you have to deal with both regular turnover and employee performance issues.