Hi Ben,
Commercial - Invoice (some pay there and then, some send cheques, 28 days credit)
Domestic (large houses) - Some invoice depending on size of building, some housekeepers need invoice to offset payment from the housekeeping accounts.
Domestic (small) cash or cheque on completion
If out leave a ticket and ask for cheque to be sent to you.
Contracts - Domestic- don't bother
Commercial - Most are happy to have a contract if it is a necessity.
I don't have contracts, never have, I always tell my customers that my standard of work is my contract, if I am good and competitively priced then keep me, if I am rubbish or too expensive then sack me!
Never had any problems with that agreement and some commercial contracts I have had 10yrs +
Good luck,
Trev