The trouble is to discern real Torah from Torah of the Sitra Achra [Torah of the Kelipot, Dark Side.]
What I mean by this is a statement from Reb Nachman that once there is found a true tzadik (saint), there come many copycats to try to get the same level of money and success they see the true tzadik got. This same idea goes for yeshivas. After there were authentic Litvak yeshivas like Voloshin, Mir, Ponovitch and Brisk, there came copycats that seem to learn Torah but in fact only learn Torah of the Dark Side, demonic Torah.
What makes the false Torah places particularly pernicious is they makes learning Torah for sincere people almost impossible.
However most Litvak places are pretty straightforward as to what they are about. If you have any kind of Lithuanian yeshiva in your area I do not urge caution, but assume it is OK. There surely are exceptions but you do not have to worry about them unless it comes to your attention.
Torah is incidentally against sin. The hope in learning Torah is know what sin is, and to stop doing it. It is not to lift up people, and to be positive and make people feel good. That is, to feel comfortable and not to feel bad about sin. There is an alternative Torah that is taught nowadays that is made to make people feel good and to get the money keep coming in. That is not the Torah of God. When you hear teaching that is against authentic Torah, run for your life. The first verse in Tehilim says "I did not sit in the seat of the scoffers." I stay away from counterfeit Torah for I am afraid of God's punishment for sin.
[Sin is incidentally, how the Torah defines sin. It is not how people try to redefine sin in order to fit their lust for money. Therefore the best way to keep Torah is to learn Musar [basic Torah ethics]. ]