A teacher who says nothing whatsoever is good to the extent that paying for a lesson motivates you to prepare for it.
A teacher who says "oops you missed some notes in that fast passage just before the recapitulation, you need to work on that" isn't telling me something I didn't know already.
A teacher who points out dynamic and phrasing indications in the music that you failed to observe is more helpful, but if you just concentrated harder you wouldn't need a teacher like that, anyway.
A teacher who shows you betters ways to move your arms and hands so that you can play a passage more easily is very helpful and worth the money you pay.
A teacher who looks at the list of pieces you want to learn and says "You might think that one is too hard for you, but it's not as hard as it looks, don't wait, go for it now," or conversely, tells you to hold off on something because it's harder than it looks, is also worth the money.
It probably takes 3 months to tell whether a teacher is helping you or not, especially if you have to decide whether advice on how to develop your technique is good or not.