When I'm playing NL hold 'em at the casino, this happens a lot: I make a big bet on the river and the other guy is thinking about folding. Then, he'll ask, "Will you show if I fold?"
I never know what to say, so I usually don't say anything. If I say yes, I'm afraid they will take it that I want them to fold. If I say no, I'm afraid they will take it that my hand is very strong. But, in either case, I'm giving away information.
What do you do?