JayWood

function add_custom_classes( $classes, $class, $post_id ) {
	if ( 'product' == get_post_type( $post_id ) ) {

		$classes[] = "sm-pid-" . $post_id;

		// Post Class on Single Product
		if ( is_singular( 'product' ) ) {
			$classes[] = "sm-product-view";
			// Post Clas Product Archives Listing
		} else {

JayWood

<?php 
function fb_1398591523488596( $classes, $class, $post_id ) {

	if ( 'product' == get_post_type( $post_id ) ) {
		if ( is_singular( 'product' ) ) {
			$classes[] = "post-class-when-viewing-single-product";
		} else {
			$classes[] = "non-single-product-page-class"
		}
	}

JayWood

<?php 
function fb_1398591523488596( $classes, $class, $post_id ) {

	if ( 'product' == get_post_type( $post_id ) ) {
		$classes[] = "my-amazing-product-class";
	}

	
	return $classes;
}