Expect it from the start, and you will be less disappointed. Look for discrepancies in the answers you get to the questions above. If you notice discrepancies, point them out, and don't necessarily believe the response you get. Just note the response for future reference. But keep that red flag up, no matter how well the discrepancy is explained.
Some people are good liars.
When you get too many discrepancies, even if they are well explained, disengage. If they all think you are going overboard, take a break for a week or two. You won't die. Meanwhile, ask around about the person who interests you. Collect data from as many sources as you can.