Like subbing for any company, read the specs, understand the specs, know what your costs are, how long you will have to carry them and when they state payment is due by.
Then double that.
If you can provide to spec and carry the costs for longer than you think you should have to, then you'll be fine. If it stretches you to provide service to those properties, at that level of spec, with long durations before being paid, then any subbing role might not be right for you at this point.
That's not specific to US Lawns, that's a general rule that applies to property management firms, developers, other landscapers, etc.