This isn’t always easy to figure out. It’s certainly a good idea to have someone try out your flute if you think there’s something wrong with it. However, people play differently. Sometimes these differences reflect the player’s ability. In this case, it is you and not the flute. In other instances, playing differences can mask a problem in an instrument. If someone can play an instrument that is out of adjustment, that could mean he or she is using air differently in the instrument. Or that person could play with a relatively heavy touch. I’ve heard of teachers who encourage a heavy finger touch in students, but today that is a rare teacher. Most flutists try to cultivate a lighter touch in order to save their hands and improve dexterity. A heavy touch also puts more wear on the instrument. I’ve seen how people who play maladjusted flutes eventually develop heavier and heavier touches. You get positive feedback when you press hard, so unconsciously or not you continue to do so and get into a viscous feedback cycle.
That being said, no two people will ever have the same touch and there is a wide range of functional finger pressure. Well-made flutes are constructed to take the punishment of many hours of playing over a lifetime. And learning to play a flute versus learning how to test a flute to find the smallest of quirks are very different ways of playing an instrument and ideally are not intermingled. It does not serve the flutist constantly to hear problems in the instrument when s/he plays; the job of the flutist is to make the flute sound great. Conversely, the repairperson needs to be mindful of not trying to make the instrument sound good; you need to find out when the instrument fails to sound right.
So if your hands are hurting and your flute isn’t responding like it used to, it’s really time to have it taken in for a look. That way you can eliminate the instrument as a problem.