Please don't use paper test strips (warning: rant)

I went to Petco to swap my dead neon tetras for alive ones (I know, cruel). They require a water sample from your tank to make sure you didn't kill them due to ammonia, nitrite or nitrate poisoning. I THOROUGHLY clean all my tanks every Sunday and test the water 1-2x week with the liquid drops from API. I went to Petco on Tuesday, an employee tests my water, says my ammonia was at 3 ppm and that my tank was overstocked! What?! Do they use those shitty paper tests on purpose to avoid giving ppl their money back? So I rush home to test the water myself and got zeros across the board. Came back to Petco with tested water in hand to get my goddamn money back. Moral of the story: Don't use paper test strips. They are inaccurate and will give you a huge headache.