Hi, Just not quite sure what you want to achieve with your disclaimer.
Who gave the instructions for works to commence? What were the agreed terms? Was this in written or verbal form etc., (write all these down)
A payment disclaimer serves no purpose now if it was not part of the original agreement nor brought to the attention of the company.
If the client is not satisfied with the works done then they can ask for remedial works or terminate your friends services. Your friend needs to set down what works has been completed in a letter to the company and ask them to respond within the next X days commenting on what they are not happy with and hold in dispute to paying his fees. Other works not indispute will need to be paid for as agreed 'on completion'.
I now tread carefully with my advice whilst I do not have all the facts ....... I suggest that you seek legal advice on how to recover monies for part or full performance of an agreement to carry out works. But some, part , reduced or full payment is recoverable. If you have any agreement to carry out works your chances of success may be high. If you have cause damage or poor workmanship the amount claim will start to decline to ofset the companys cost to putting it right.