Urgent help needed please!

[tigwig]

My hubby has just received a letter via recorded delivery from the daughter of a family member he has recently built a garage for.
The letter is basically saying they have had several inspections from builders and the roof and floor is unacceptable and the case is being referred to trading standards and they are getting an independent report done which they will be claiming back the �400 cost from us. Then if we don't cough up they will take us to the small claims court.
She then goes on to accuse us of taking �1500 of her mum's life savings and says the paving is unacceptable too. All this is untrue.
The letter is not well presented and I am unsure whether she is testing us or not. Is there any way to find out?
As far as my hubby is concerned he did the job to a high standard and he has all receipts to prove the cost of materials etc. He worked like mad on this job, the woman was a nightmare from start to finish and has done this sort of thing before, he ended up hardly earning anything.
They did recently contact him before complaining about a minor problem to do with the rain water collecting or something (sorry I don't know exactly) he said this wasn't caused by anything he did and offered to solve it for free as long as they provided materials but they refused.
I know what this sounds like, he is at fault and a cowboy but this is not the case at all. Please I don't want any sarcastic answers just advice on what we can do. You hear of people being ripped off by builders but what happens when customers take innocent builders for a ride?

[tigwig]

bednobs I didn't mean she had no idea about the quote, obviously he had gone through and gave her a copy of the first one it was just when she changed her mind and added more expensive things he didn't put it in writing especially with her being family and everything.
A lesson has been learnt from this - stop being self employed cos its ****! Its been nothing but trouble from day 1 aaagh!