Store owners can clear the cache on their web browser to see their updated banners on their stores. However, it would be rare for a customer to clear their cache to see the updated banner. I know when I have designed websites for people, I can see the changes, but, they can't until I flush the cache for the website I'm working on. That forces their web browser to cache a new page so they can see the changes. Perhaps the cache flush when the banner is updated on Zazzle is not working? If it was, changes would be seen immediately I believe.
