id keep it simple whether domestic or commercial, when i clarify the job they want and what i can offer with price and they agree i cover the options of payment methods.
then ask which payment method they prefer, then clarify that we dont need paying until the job is complete and they are satisfied.
i complete the job check they are satisfied give them my bank details if asked for bank transfer, or stand there all expecting like (once all kit is loaded back into van) and say well were all done here was it cash or cheque, if its cheque if you can make it out to my company name....usually does the trick. if theres no payment after 2 weeks for domestic 3/4 weeks if commercial, i just call and say hiya i just wondered if there was a problem with the clean as ive not received payment, is everything ok?
if ok (yet to have one thats not) thats great could you tell me when you expect to arrange payment, as i like to keep my accounts in order month by month ideally.