Spotting someone who lies is not an easy task, especially when it comes to online dating. It is hard to figure out someone who is lying if all you have to go by is just lines of text and your personal good faith. The prisons are full of people that still claim they never did it, yet they were nailed by everything under the sun.
In dating, you will have people make claims and pretty much refuse to take responsibility for any actions they have caused. In order to spot a liar, you need to find out is this person being an open or closed book with you. Being a closed book at the time of dating is normal; folks will be pretty shy and will want to wait until that right person comes along to open that book. But if you have been seeing each other for weeks and you have not gotten past page 3, then something is up. If you always ask to see their car or their house months after dating, yet they do not show it to you, then you should feel that they are trying to pull a fast one on you.
It is hard to confront someone who lies to you, so it would be just best to press the issue once and call it off if you do not get the answers that you wanted.