The rule is that there is no advertising, within posts, allowed on the site. A thread that is started that says something on the order of: "Book with Joe's Travel" will be immediately deleted.
The "rule of thumb" and it is open to interpretation of the moderators so it isn't etched in stone is: "If it is a direct answer to a direct question then the name of an agency or tour provider can be mentioned." I.E. "Does anyone know of a good agent or tour provider?"
This gets abused by agents and tour providers who register under a couple of ID's and start a thread and then answer it under another userid. We can tell when this happens.
So: If someone asks a specific question you could say that you were able to get a great deal through Overstock or Ebay. But do not provide any more specific information such as contact information or website URL or the post may get deleted.
However, I would advise anyone who does book this way to REALLY pay attention to the fine print and price compare. Current cruise line regulations do not allow any agency to sell a cruise for less than the current price the cruise line is selling it for. Also, the 50% or 70% off is very deceptive. They are talking about the "nobody ever pays" brochure price and not the current selling price.
We want to provide the free flow of information but also don't want the boards to become nothing more than a bunch of advertisements. It's a hard line to walk and sometimes legitimate information is deleted with the overt attempts at advertising.