Working With The Public

The people who come and apply for welfare are called 'clients'. The clients fill out an application and then see an intake worker (me) and go through an 'interview'.
Paperwork, computer entry, more paperwork, question-and-answer time, end of 'interview'.
That's how it goes, every day. Three to four interviews a day. I meet some interesting people.

Today, I met a client employed where I used to work. I got to ask her about all the gossip I've missed since I quit. Then I had a horrible coughing fit all over her. Welfare Healthcare time!

My last client of the day cracked me up. He told me, "They told me to lie about what I have, but I'm not a liar, so I have a bank account in Nevada. Should I have not told you that? What would you do if I didn't tell you? Can you find out that stuff?"

First off, I asked him who the "they" was that told him that.
"Some girl," he told me.
I then told him that it was always better to tell the truth, most of what clients lie about doesn't matter anyway, and yes of course I can find out that stuff. He relaxed a little. And then began asking more questions about being truthful! I finally told him that it would be better for him to tell the truth and see how it affects him, rather than go to jail for perjury. Then we had a little talk about Welfare Fraud.
When I'm done with the interview, I give him a paper that he needed signed by his roommate.
He asks me, "Do they really have to sign this? How would you know? Can't I forge it?"

Why are so many compelled to be truthful about lying?