"Note: PM privacy is not guaranteed. Encrypt sensitive messages."
Seems the forum policy is that PM are personal messages and not private messages.
"Haha, you trusted me, you idiot!"
You have just validated every bad thing everyone has ever said about you.
Well, from the PM's he posted it's not quite like that in Goats case. Ask for agreement on confidentiality THEN send the confidential information in a separate message afterwards.
The following is how to create an agreement:
Alice: "I'd like to keep this confidential, is this OK with you?"
Bob: "Yes"
*Conversation ensues*
The following is how to create a silly situation:
Alice: "I'd like to keep this confidential. I've just taken advantage of Carol, she's such a sucker"
*Possible Drama in the making*