The more items we have, the more eager we are to complete the series.
People like to collect and complete the set. Incomplete puzzles or images are a nag to our brain. Can you divide your product range into several (logical) groupings that people can 'collect'? Or you can show them together to suggest the items being in a set to stimulate people to buy them all. You can show sets on your webshop, or e-mail people that already bought item A an B that they really should buy item C to complete the set!