Scott, it's one thing to request services from others. Advertising your own services in an entirely different matter. If you want to sell a product or your services, you can purchase advertising space like any other firm would be expected to do. It's a pretty simple concept.
Frankly, I don't think the 3D Warehouse would be a good place to advertise a product you want to sell. It's not the place folks are likely to look if they are searching for your product. And if you put a SketchUp model of the product on the 3DWH, anyone could download it and use it to make their own copy of your product.