Agree here,,
after several years, and countless disputes like these, im getting to that point where I rather have them buy the string; less headaches that way..
I rather players do not supply the string, as I have no idea how well it was stored. I had one player open his car trunk, had a bag in there with old string where the packaging was cracking, strings were all brittle. I strung up a couple racquets with that for him, and explained to him no guarantees as strings brittle, he understood, and shortly later complained one racquet string broke early. Then came back and wanted me to string more with that bag of junk old strings. I told him to find another stringer, as he did not want any other option.
If I supply string, I know how it was kept, as I do not want to waste my time with problem strings.
If anyone does supply me strings, they get my policy on no guarantees, as stringers should have a policy as such.
Also like Irvin comment above. I had a player supply me a set of VS gut to stringand fortunately I check gut out before I even use it and found a defect in the string about 3-4 feet from an end. I returned the string with his unstrung racquet, and told him to deal with it returning it to where he bought it as was not my responsibility. Nerdless to say he was pissed, but such is life.
With gut strings I clamp one end on machine clamp and walk back the string with fingers checking to see if string okay. Glad I do that as that was only time I spotted a defect on a set of VS, and was glad I noticed that before I started.