I did a job for such a shop the other week, took them 4 weeks to pay after telling me that they had sent a cheque in the SAE that I provided (that cheque NEVER arrived).
Read in local paper last weekend same shop had had a fire and had been closed for a week for cleaning, did thay ask me to do the carpet again?? NO, if they had would I NO.
If they had tpld me the truth about payment, I would have done it for FREE, but remember 'What goes round comes round' and in this case it was 2 weeks.