Watches for Sale are offered by dealers, while Private Watch Sales are offered by individual collectors.
Watches for Sale section - a couple of dealers who contribute to the forum and sell some interesting, relevant pieces, interspersed with a lot of dealers who contribute little and list pages and pages of uninteresting watches, which makes it a pain in the arse to find the few dealers who's stock you want to see. Private Watch Sales - interesting and generally nice watches sold by collectors.
I would really like to but there's actually some complicated issues behind why we can't as we're not able to change it without the URL for the topic also changing and that creates some serious knock on effects.
I defy anyone who reads this forum for the first time to tell me they really can't work out for themselves what these two titles mean. It is true it took me 30 seconds, I see no need for any change.