Squeaking: Squeaking may occur when lubrication has dried. This does not affect function, but if it bothers you, you can spray WD40 or other lubricant on the metal screws, metal hinge, springs, and metal shank to lessen the squeaking.
Replacing Parts: Plier parts will wear out and will need to be replaced periodically. If your pliers have been working well for quite a while and then they don't seem to press down hard enough anymore, or you start having trouble installing the same snaps on the same material that you have always used, it may be time to replace the parts. Replacement parts are available here.