Putting aside emotions and what you/we ourselves consider acceptable and would/would not do, taking a dispute to court should be the absolute last resort.. a Judge will not entertain an application where there has been no attempt to reach an agreement between the two parties..where there is documented evidence that attempts to reach an agreement have been made but have been unsuccessful, a Judge will consider whether the disputed work is considered reasonable or unreasonable for the monetary amount being claimed and will require independent documented supporting evidence.. i.e. if you pay someone £5 m2 it is unreasonable to expect a high quality finish, if you pay someone £50 m2 it is reasonable to expect a high quality finish..
Reputation is very important...businesses of all sizes can go under if their reputation is ruined - remember Ratner Jewellers? - so you have to ask yourself 'do I have a strong case and if I do not resolve this amicably, 'is my business going to suffer in the short, mid and long term?' Equally, you do not want a reputation of being a pushover, so it's a fine line to walk..
Consumers have rights..if a client is unhappy with the quality/
standard of workmanship, they have a right to ask for the work to be rectified within reason i.e. in line with what they are paying for the work. They cannot get someone in to rectify your work without first giving you written notice that they are unhappy with your work and want you to rectify it within an agreed timeframe..
Tradesmen have rights..if you cannot reach an amicable agreement with the client, you have the right to take the matter to court and/or to undo/remove the work and cancel the invoice, but you will have to consider costs, chances of success (in court) and how this might impact on your reputation and future business.
My advice is that you need to talk to your client about their complaints as a matter of urgency before the situation gets out of control...good luck