Sometimes you have to accept you can't do something even if it means losing the work.
You can't own a problem as the customer will soon change if something goes wrong.
I had a lovely big sofa/suite job before Christmas - lots of chairs/sofa's - they called, wanted a price on the phone which i did and they also wanted it protected. Great - good earner. But i told them i wanted to see the upholstery before i booked it in - i knew from where they were and how they spoke it could well be a fine fabric suite.
Went to have a look - it was a Duresta suite - no labeling of what the fabric was but the spidey senses told me it was a possible problem. I took a photo and found it on the Duresta site - 80% Viscose! I declined the job explaining why - now they hounded me to do it but i stuck firm - no matter what they said about it would be ok if it went wrong they can all of a sudden change when it does and its not worth the problem whatever the job ticket is.