The best and most succesful vendors around here tend to be those whom take hands-on approach to Poser.  Most of them have started off with making a few freebies first to get the feel for the market and what it takes to create a poser friendly item.
Also, look at the products you may be competing with, for example, 'cycloramas' and skydomes.

For example, a cyclorama is very similar to a skybox, and something many poser users are familiar with. There's a pretty decent number of free textures available for it: http://www.renderosity.com/mod/freestuff/search.php?section_id=-1&query=cyclorama
and in marketplace: http://www.renderosity.com/mod/bcs/index.php?Start=1&SearchTerm=cyclorama

Hi, my namez: "NO, Bad Kitteh, NO!"  Whaz yurs?
BadKittehCo Store  BadKittehCo Freebies and product support