The issue here is that search engines consider the following two locations as distinct pages:
http://www.mysite.com/products
http://www.mysite.com/products/
In the case above, the solution is simple and many posts offer such a solution to add a slash to the end of the url. But, what happens when you have the following?
http://www.mysite.com/page-without-extension
This is an actual page (not a folder or directory) which simply doesn't have an extension (common in many Content Management Systems). Your global redirect commands will force a redirect to the following, which would return a 404.
http://www.mysite.com/page-without-extension/
In this case, we'll want to specify manually which locations should be given "the slash treatment". Note, directives below are for the Apache web server (you can place these in a virtual host stanza, or in your .htaccess file)
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !\..+$
RewriteCond %{REQUEST_URI} !/$
RewriteCond %{REQUEST_URI} ^/(products|services|about|contact)
RewriteRule (.*) http://www.mysite.com$1/ [R=301,L]