Selling award tickets violates the rules of all frequent flyer programs. Using a purchased award is illegal in California, under a statute that makes it illegal to use a ticket in violation of its terms and conditions.
People on these boards appreciate the fact that Randy Petersen makes them available to the frequent flyer public free of charge. He depends on the airlines' good will for the survival of his business. Therefore, most of us won't do anything that could get him in hot water with them. Making suggestions on how or where to sell award tickets falls into that category.
Aside from that, the risks of buying and selling awards (you get your account closed and lose all your miles, they get the ticket confiscated and have to buy one at the walk-up price or stay home) are why you've seen such low prices. People won't take the risks unless there are enormous savings. What with discount fares, Web specials, legitimate consolidators who buy in bulk, Priceline.com and more, most people will just buy an inexpensive fare and avoid any worry.
And keep in mind that if you find a site, chances are the airlines know about it too. Your "customer" just might be an employee.