Ian I have only read you Q&A page at the moment, Just have a read of what you have in one of the answers.
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We ask for payment to be sent within 48 hours of cleaning, if you are away call us when you get back to let us know payment is going to be late, if there is any problem please call us (we dont bite) if payment is made later than 21 days you will be charged a £2 late payment fee. Payments that continue on to be late will have services suspended till arrears are paid in full and the next clean is paid in advance.
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This is the way I would word it.
We ask for all payments to be made within 48 hours of Completion, If your were away during your clean, then please contact us on your return.
If there are any problems, then please contact us, we will endeavour to rectify any problems you may have.
If payments are later than 21 days, window washers reserve the right to charge a £2 late payment fee.
Any client with Continued late payments, may have there service suspended, until full payments are recieved by our office, Window washers may also ask, for advanced payments for future cleans.