You may also want to rethink your heavy dependence on this type of business. Possibly you can recruit some other residential or commercial work that would pay better and keep the cash coming better.
Do these accounts make more money than average? Do they lead to doing work for the new buyer that you can retain?
I think you have to work on the terms up front. Possibly another company that does a lot of this stuff can respond here with an up front solution.
My contention is that your problems (client) should not be my problem (contractor). A solution must be found unless the rewards are great and the end justifies the means.