I took in a pair of raw denim jeans to have them hemmed, as a test run, to make sure they wouldn't destroy my favorite pair. Everything went fine, but on my second trip I wasn't so lucky.
My second trip, I took them two pairs of raw jeans to have hemmed and they creased both pairs up to about 6 inches from the bottom. One of them came back with rather large distance from the hem to the stitching and the selvedge lines were squished together on the inside.
They effectively destroyed about $400 worth of jeans. Do not expect repeat visits to run as smoothly as new customer visits.
*I'm editing this to add another star because no irreversible damage was done to my pants. I managed to fix everything with an iron and some patience. I probably wouldn't worry much about bringing traditional menswear in for alterations. Still not particularly impressed.