There are a few things you can do to minimize your exposure to “non payers.”
The first and foremost is to provide a service that goes beyond what the homeowner / property owner expected. That comes from a few methods. First, don’t over-promise to get a sale. Be upfront and point out where you may not be able to clean well and why. Properly done, you’ll come off as a seasoned professional that knows what you’re doing, and you’ll simultaneously set expectations for your client correctly.
Second, over-deliver somehow. Each job is unique, and you’ll have to figure out how /what you can do, albeit the idea is to provide a little extra “wow” factor they can talk about and make them “feel” they received more than expected and real value.
Third, and this is always key, make sure you’re communicating well with the client to remove ambiguity. Some people you have to more or less force (poor choice of words, maybe coaxed is better) what they’re looking for so that you know you can meet their requirements or not. Having a work form that goes into great detail with check boxes can not only help eliminate ambiguity, it can help you upsell.
Contracts don’t need to be in writing to be enforceable, albeit unless you have a long-standing relationship with the property owner/manager, you’re setting yourself up for misery if you don’t use well-defined contracts. They don’t need to be drafted by a lawyer, and Google is your friend when finding templates to use, however, most county bar associations offer one night a month where anyone can talk to a lawyer for free (usually at a library or similar) and that can save a new business some bucks. Lean on your insurance agent for help there too. Your contract can help mitigate risk, so they should be more than willing to discuss it with you.