Actually no, I don't tighten my knots with pliers, not only because of the problem you mention but because it would be a pain in the ass.  My point with gripping braid was only to address the fact that quality pliers, whether for fishing or any other purpose, should close tight.  In the old days that was a given but these days, more often then not, the quality of manufacture isn't there and neither are the tolerances.  If you want to get an idea of the quality of a pair of pliers checking the tolerance in the jaws will give you some clue.