I watched the beginning and some at the end. I just string racquetball racquets but noticed....
1. You forgot to use the support adapters at the head and throat. The metal on the posts could damage the paint job on the racquet.
2. Didn't look like you cinched up the tie off knots correctly.
3. Careless with your pliers in pulling on the knots and throwing it on the racquet bed. You could really hurt yourself.