The general rule is that if a player answers that they are willing to show that they are not as strong as they could be. They might still have 'a' hand, just not a monster. Player's don't generally want to show another player that they made a 'good' fold.
The opposite tends to be true if a player suggests that they will show a player their hand if they fold to a bet. It's human nature to say the opposite of what you want the player to do .. it's like a challenge. So when you hear a player say "I'll show you if you
FOLD." they want you to call. If a player says "You're not
CALLING, are you?" or "I'll take a
CALL" they usually want a fold. Notice that the 'call' statements are opposites, but the word 'call' is what I look for and therein lies the challenge to the opponent to do the opposite, fold. GL