what to do?

[Ummu Sufyaan]

you know when someone is doing something wrong, like lying/deceiving people and the people will fall for their tricks, and you need to warn/advice people about this person because their fitnah if you will, is kind of bad. but because they are so clever, they cover their "tracks" well... so basically you have no evidence of what they are doing, but you know that they are doing wrong, just simply because something really isnt sitting right, etc.
now obviously if you need to warn people, then you need more then that to convince them and even more so, because you could be in the wrong.

well yes, what do you do? how do you get your evidence?
this thing that this person is doing, is really bad so it cant be ignored.

should i so about advising the person instead? what if this person is a male/brother?

daym this is so confusing and hard

[Dagless]

If this thing is so bad then why is there no evidence?
If the person you want to warn asks, you could maybe give an example of this persons previous 'victims' as an example? Usually if the person is close to you then they should take your advice or at least be more cautious. That maybe enough to save them.

[Muslim Woman]

....but you know that they are doing wrong,

how do u know ? We must be careful about backbiting . Unless if u have proof , may be it's better not to tell about him/her to others . And keep praying for him /her so that s/he can overcome the fault.

[Rafeeq]

Akhti Ummu Sufian,

I can understand your feelings. It happens with my and it is very embarrassing. But I would like to suggest you to think positive. This is what I try to tell myself too. If some one is really wrong, his wrong acts will soon come out. One can not remain hidden for a long time.