Thread title says it all. If you come across any sort of bad stringing practises, this is the place to post it.
I'm going to start it with a racket that I got from a clubmate to string it which has made me speechless. At the first glance it appeared that one of the grommets was somehow capped. It turns out that there was a steel nail that was pushed through the grommet along with the strings and clipped flush with the frame on the inside:
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The BC chamber of stringing horrors