I would say that it's typically assumed that there are confounding factors in any experiment. An experimenter has to try to minimize that, but you're still not

I would say that it's typically assumed that there are confounding factors in any experiment. An experimenter has to try to minimize that, but you're still not going to be able to replicate a full experiment. If you have more than one researcher administering a test in a stereotype threat experiment, that'll reduce the likelihood of that being the confound. If other studies (not replications, but their own experiments, with their own, different approaches to study the problem) agree with the first experiment, the effect is likely real. I would also say that you're viewing the entire system far too antagonistically. Nobody goes into academic psychology to get rich off of it.