Try removing the if statement around it that says "if there are no products, show the featured products".
So:
{if $products eq ""}
{if $f_products ne ""}
<p />
{include file="customer/main/featured.tpl"}
{/if}
{/if}
becomes:
{if $f_products ne ""}
<p />
{include file="customer/main/featured.tpl"}
{/if}