my position has always been that if you have books to sell, get your together before you start your thread. the best sales threads here have always done this, i don't know why some people should get to make announcements beforehand, unless it's an hour before.
i don't want six or seven announcement threads pushing actual sale threads down. i don't want people griping about announcement threads that never turned into actual sales because the announcer got busy, forgot, got pm offers prior to the thread starting, or whatever. the idea of giving people a couple of days advance notice is great, but why not put it in General? Start a thread saying "I'm getting books x, y and z back from CGC in grades a, b & c, and will be selling them in the marketplace in n days. pm offers seriously considered. don't clutter up the Marketplace - a venue for selling, not advertising - with "COMING SOON! THE DINGLEBERRY COLLECTION! WOW!" &etc.