True and false predictions are the most obvious way to judge a prophet, but not the only way. A prophet is much more than a fortune teller. He's a conduit of messages direct from YHWH. As such, a true prophet teaches obedience go God's commands, blesses whom God has blessed, and curses whom God has cursed.

A prophet who is true this year, might not be next year, but a prophet who was false last year will always be false. He might repent, but he will never again be a qualified prophet.

Balaam appeared to have been a true prophet at one time, so what went wrong with him? Nobody is flawless. Even a pastor, rabbi, prophet is susceptible to greed. #balak