IMO, if you can figure out howsomething is done, then you should feel comfortable performing it, but if you know its anot persons trick, just dont claim ownership or creation of it, give the author their just deserves and point them to the right place. It might also be worth buying a trick you figured out, since reguardless of the fact you didnt need the instructions, you are still using a trick someone worked hard to create, you learned it from or vicarious though them, and this is a good gesture of thanks. I know i figured out the Dresscode routine watching it, i still dropped the cash on it because end of the day, its something fun it made me smile, and that was worth my money.
I feel this is especially important if your earning from your performing. again, its all down to how you feel as ethics go, personally i feel magic is a endagered animal these days with how easy it can be to whip a phone out and dispel someone, so those who practice, great or small, should stick together. To that, if you can make an earning off something a fellow practitioner created, help repay them. That trick could help earn you an unlimited amount of viewage or earnings, the price of gratitude is one time.