What would you do - dodgy builder

Had a phone call from a regular customer telling me the builder who's doing her extension said there is no grommets on the existing sockets (which we fitted re wiring the place 18 months ago).

At first I thought there's no way we hadn't put grommets on but further through the day I started to question the lads work and thought maybe one of them had just forgot to put them in. I always check the lads work but with it being months and months ago slight doubts started to creep in.... She's a regular customer, why would she lie???

Anyhow I went to the property last night to inspect all backboxes. I was there for two hours walking around with customer. EVERY single back box was grommeted through the entire property except (conveniently) 2 sockets and a light switch on the existing part of her kitchen which they are adding to.

It gets worse..... The builder had told her that she wouldn't be able to sell her house if there was no grommets in!

Long story short the builders price was inclusive of the first fix only (he's not part p registered) however he's an "electrical engineer and he's really good". He was going to get his mate to sign it off. But home owner said she would ask me to second fix. I've gave her a price.

Basically I think he's tried to shaft me to get the work. How convenient that those sockets that he opened up didn't have grommets on? He also plastered the sockets in the wall yesterday without putting any on. Making my life difficult to put them back in!

I can't see any routes he's ran his cables etc. I like the lady we've done lots of work for her but on this occasion I might just say thanks but no thanks. The phone call I received was of a frightened woman making accusations. I questioned the standard of my employees workmanship etc etc

in this position what would you do?