Personally, I think the quilt shop sounds very unprofessional. The comment about the quilt "falling apart" is ridiculous. I have made quilts by hand sewing everything and those quilts have been drug all over the world by my great nieces and they have not fallen apart - one is 5 years old and one is 7 years old.
i would think your machine sewing would hold up better than my hand sewing for sure.
the quilts that I make are far from perfect, but they hold up.
too bad because I don't know how you would reassure your customer