The number of products that you see per page on the results is controlled by this line of code near around line 147 on my Products_Results.php page:
$maxRows_WADAProducts = 5;
To have users select how many to show you can add in links like this toward the top of the results page:
Results per page: <a href="Products_Results.php?num_results=5">5</a> <a href="Products_Results.php?num_results=10">10</a> <a href="Products_Results.php?num_results=20">20</a>
Once you have added the links you then need to update the line of code that controls the results per page to look like this:
$maxRows_WADAProducts = isset($_GET['num_results'])?$_GET['num_results']:5;
The page will still default to 5, then the user can click on a link to show the number of records they want. The updated code for the $maxRows will check to see if there is a number of results URL parameter and use that, if not it will default to 5.