Gotta knock a little harder

<?php if (is_single()) { $posttags = get_the_tags(); ?>

<?php if ($posttags) {
	foreach($posttags as $tag) {
		$string .= '<a href="' . get_tag_link($tag->term_id) . '">' . $tag->name . '</a>, ';
	}
	unset($posttags);
	$string = substr($string, 0, strlen($string)-2);
	echo $string;
} ?>