Shower issue

[hammers4spanner]

Had a call earlier today saying I've caused a leak on a triton mixer bar shower because i forgot to fit two washers. I fitted it last week and at the time i left nothing was leaking ironic that i also checked the dial at the meter and all was good there as well.
Customer phoned and said they noticed damp appearing past the tiled cubicle first and called the builder in ,and from that point it has been said that i didn't fit two washers.
Now the only washers i can think of are the two on the nuts behind the shower mixer bar.Now i remember dropping one when fitting it and picking it up and putting them in again. Problem being is that they are saying that the whole wall is now damaged tiles /plaster board stud work needs addressing but i have been called after to say its my fault .

Initially i said ok apologies etc but after thought is hang on a mo so what you guys think?

 

[Best]

I do the same, compress and check but then I`m just paranoid about the little blighters leaking tbh.

I am afraid a pipe will pull out of a fitting, that's why I check them and then paste and retighten. It was the way I was always taught and it has allowed me to stand by any compression joints I do and I don't worry later. If a joint did have a slight weep when water turned on, it just needed slightly nipped up more.
I would rather have confidence in the work I can visually see, rather than just using my experience of 'feel' of how much to tighten a nut. We can all make mistakes otherwise.