I found a small V-shaped snip in the border of a customer's quilt when I was quilting it - of course, it was the last border to get quilted. I took a picture of it and emailed it to her. I knew I hadn't cut the fabric, but I offered to have it stitched closed by a professional appliquer here in my town. It was less then 1/4" on each side of the V. She opted to do the repair herself.
I did cut one of my own quilts when snipping thread - nice little circle! I was so grateful the quilt was mine, but it still made me mad at myself. I am extremely careful since that accident.
As a "professional" longarmer, I would be extremely upset if I ruined a customer's quilt. I know the amount of money and time involved in every quilt...my quilts all have, literally, blood, sweat and tears invested in them! I had a longarmer ruin my very first quilt...that's why I bought a longarm 9 months after I learned to piece.
Quilty hugs!!