Judging is a skill that comes with experience. The more you talk with others, the more you will be able to judge them. So, at first u can concentrate on how to find persons whose profiles "seem" to be convenient for your needs : u may start asking urself: will they be able to help me? can I provide help in return?. later on, you will find out with whom u feel more at ease and you will find it easier to decide whether they are or u r of any help to each other. I personally have two important rules: 1- Do not rush to make judgements. Give urself and others time to know each other better 2-but just be cautious: do not disclose personal info about urself. Sometimes it can be really dangerous. Good luck!

Try to talk to them like sending messages if they are sincere before you judge them, also keep some precautions. There are a lot of people who are sending spam messages such as recruiting you to join their company or persons sending love messages to you. They are not real and never dare to reply at them. All they just want from you is your email so they could spam it as well or something. Try to see their profile most of them don't write something on their profile they just join italki to send spam.