I have experienced gravity acting to pull objects towards the earth. You claim to have experienced gravity acting to pull objects into the sky. Therefore you are deluding yourself.

I'm not arguing with the conclusion (!) but I think the use of "therefore" is misplaced. There's no logical path from "I have experienced X and you have experienced not-X" to "you are deluding yourself" -- it's just that we happen to know enough about gravity etc to know that the person who claims to have seen it work backwards is probably mistaken, lying, mad, on drugs, etc. The handwavyness is around the shared assumptions that it's okay to take as a given... which mostly depends on context.