I've had friends and romances online. Can't say they've all been liars. In fact only one did I find to be a liar.
I've opened up to numerous people online with no issue.
Know the Actual rules for online dating and don't he afraid to check people out.
My current gf, who I met online, was bothered by my caution of her being who she claimed, at first. Over time I became convinced she wasn't lying. A person who is secretive, seems to be hiding you, not very open about their life, etc... are red flags.
My gf, on the other hand, was open about her life and the people in it. And thus it became evident she was who she claimed.
Also she has since seen episodes of Catfish and now understands my initial skepticism.
Really there are ways to go about things without judging everyone as a liar.