I didn't see this suggestion, but maybe I'm blind. xD;

So basically this is a bad mockup but I hope it gets the point across. I couldn't figure out the font used here after a good minute (>_>) of searching. XD

Basically if people like me make private trades, lose PMs, etc. and don't name them to a T., it'll be an easy way to see who exactly it's for. Or in case they make a private trade + copy/paste or type the wrong number. I made this trade a long time ago and had to cancel it. Thankfully the user reached out to me!

I hope it wouldn't take all too much effort, but it'd be a simple fix. Also a guarantee to see your trade is properly private to the correct person without going to sent messages to either see the message to the wrong user or nothing at all.

Would have the person's ID that it's private for. That is all!

Edit - Additional suggestion to add to by Lex (#56485)
"What about adding another section to the TC where your private trades will show up, along with the message links we get now? Like a tab inside of the TC where it says "Private trades" and when you click it it's every private trade you have pending either for you or from you."

More or less another tab where you can find trades made by you for others, and for you by others!