Something changed with the site in the last couple of years. So while you can initially search a single sellers inventory, once you're in the results, it will always revert your searches to all sellers. You either have to go back to that seller's "home page" and search again, or with each search. you have to keep going back to the seller list and deselect "All Sellers" and filter by the one seller you want.
Here is my dealer page:
http://www.sportlots.com/inven/invenbin/dealerpage.tpl?dealer=daclyde1
Just swap out "daclyde1" with any other seller IDs to get to their store page.