Just a couple of pints on this thread, if I may, firstly I think it only good practice to obtain a credit report on any new customer, this would mean that you have at least some idea of what you are getting into, regarding payment waiting time etc, this does not have to be an expensive process, and will protect you against the vast majority of problems, be sure to run regular credit checks on all of your existing customers at least annually!
Secondly, never, ever, start a contract without getting them to sign your service agreement, making sure, that you win the battle of the forms, this basically means that they accept your terms & conditions over their own, assuming that your contract is governed by the laws of England/Wales?Scotland etc, this should protect you in case of a breach of contract.
In order to be seen as a professional, it is necessary to act like one, most clients will be pleasently surprised by this sort of attitude, as a lot of clients/prospects think that cleaning companies, especially the smaller ones are not very well run, and quality is a pipe dream for most.
This is my opinion only, and the above is not intended to cause offence to anyone, regards.