If all it takes is one person’s experience to disprove something that everyone else testifies (with evidence) is a hoax, that really opens up the marketplace!
But seriously, taste is not that subjective. That’s why words like "peppery" or "bitter" or "goopy," etc. are understood. We share a biology, we share cultural norms and history, and we share language. Not exactly, of course, but enough to make judgements about taste or hoaxes with sufficient objectivity for them to be understood as binding. Are there lots of debates at the margins? Sure. But the fact that there are fuzzy sections along a line of discrimination doesn't eradicate clear demarcators.
So, the question as to whether there are "hoaxes" can, at least sometimes, be resolved. If you disagree, the next time your mechanic tells you that he chased gremlins out of your engine and charged you an extra $500 for that, you’ll have to pay him. Because if you cry "hoax" and all he has to do is testify that he saw them, you’ll lose the argument and be out $500.