You build a relationship, listen to what they say, take it step by step. Some things might be verifiable. Ultimately you either believe them or not. If you believe them it's either based on trust or by having verified. It's wise to move slowly. Over time you will have a pretty good idea whether or not they're trustworthy.

If they say they are hot or rich they are lying.

Any relationship that lasts more than two days, You get to know the person. Unless they are a pathological liar you can get a pretty good idea. Nobody's perfect, if everything they tell you seems like its perfect or meant to impress you, You can bet they are making it up. Watch the video and see http://www.youtube.com/watch?v=7GcVnhNjWV0

The only way to assess it would be to make groups of types of facts which you are questioning. Claims about lifestyle which are beyond a normal persons means I would say that the trust is in the proof. Claim about ones self and their own personality can only be trusted when compared to the actions they take when they aren't talking about their own qualities. Personal appearance and things of that nature can be proved pretty easily with a webcam or regular cam, like have them do something that validates its authenticity (have them write something on a card or pose a certain way) Truly the only thing I care about is that the person is the gender they say they are, aside from that I generally don't care if what they say is fact or fiction, because no matter what it is about them as a person. If they lie about having something, its probably because having that thing would make them feel more like they want too about themselves. Or if they say they possess a quality they don't its probably because they wish they did. Of course some people lie because they are trying to tell you what you want to hear, but this is the internet, truth is relatively unimportant on the grand scale. As long as you aren't putting yourself at risk by giving out personal info or meeting them you should take them at face value, but if you are expecting a more intimate relationship with them you should talk on the phone, validate their identity with either a picture of video, and dig for as much evidence of their identity as possible. Everyone is bound to make little lies about themselves, just don't trust the people who make the big lies I guess.