It is one of those potentially awkward questions - a candidate has no obligation to answer that question, and in some cases, I believe it is even illegal to ask.

It's not illegal in the US to ask what a candidate is getting paid, but you also (typically) have no good way to verify their answer.

It makes more sense for the person you are asking to lie in order to receive a higher offer.

I know I've done that before, even at the negotiating table. "I'm sorry, I can't accept this offer. I'm making more than this currently."

Why would they tell you? Unless you are in the process of actually making them an offer, you are just some random stranger asking personal questions.