One example: people maliciously steal pictures to use as their own. If anything, this is one of the main things I think about. People will always know what it was about. All the replies show the original subject.
The issue I see with this example is that people here request the BTCtalk username and date as part of the picture taken, meaning the pictures by themselves without this won't really carry any weight here.
Correct, its actually good practice to post images with a date and username, most people
do anyway.
As for deleting posts, I find it annoying and it can prove difficult I imagine to verify certain
facts in the future.
If people are worried about privacy they can always buy items anonymously, obviously that
wouldn't work with raffles and auctions.
But in traditional auctions can't people bid "over the phone" so essentially their identity
is only known to the auction house and eventually the seller. Could something like that
work on the forum?