Boats for sale isn't reserved just for dealers, it's reserved for supporting members. If you've made a contribution to the TFF you have one of the large blue icons by your name with your support level indicated. Once you've done that you can post on the boats for sale page.
If you don't want to make a financial contribution to the forum, you can post on the swap/sale page and bump your post back to the top every 4-5 hours.
Here is the post from the News/Info page regarding supporting memberships.
http://texasfishingforum.com/forums/ubbt...hips#Post732421