From an SEO perspective, it may be negligible if you include a trailing slash for directories or not, as long as you set redirects to the chosen one (to avoid duplicate content) and link-build to the right one:
Other authors suggest that it's best to avoid a redirect and that a trailing slash is typically for directories (folders), while a lack thereof implies a file.
But what about the user's perspective?
Is there any research on the best practice? What do users expect? (If anything.)