Only allow users to use the trial level once with Paid Memberships Pro.

my_pmpro_after_change_membership_level.php

<?php
/*
	Only allow users to use the trial level once.
	Add this code to your active theme's functions.php
	or a custom plugin.
	Be sure to change the $trial_level_id variable in multiple places.
*/
//get trial level ids
function my_pmpro_trial_level_ids() {
	// edit this to be a comma separated list of your trial level ids
	return array(1, 8, 9);
}

//record when users gain the trial level
function my_pmpro_after_change_membership_level($level_id, $user_id) {
	$trial_level_ids = my_pmpro_trial_level_ids();
		
	if( in_array( $level_id, $trial_level_ids ) ) {	
		//add user meta to record the fact that this user has had this level before
		update_user_meta($user_id, "pmpro_trial_level_" . $level_id . "_used", "1");
	}	
}
add_action("pmpro_after_change_membership_level", "my_pmpro_after_change_membership_level", 10, 2);

//check at checkout if the user has used the trial level already
function my_pmpro_registration_checks($value) {
	global $current_user;
	
	$trial_level_ids = my_pmpro_trial_level_ids();

	if( $current_user->ID && in_array( intval($_REQUEST['level']), $trial_level_ids ) ) {
		//check if the current user has already used the trial level
		$already = get_user_meta($current_user->ID, "pmpro_trial_level_" . intval( $_REQUEST['level'] ) . "_used", true);
		
		//yup, don't let them checkout
		if($already) {
			global $pmpro_msg, $pmpro_msgt;
			$pmpro_msg = "You have already used up this trial membership. Please select a full membership to checkout.";
			$pmpro_msgt = "pmpro_error";
			
			$value = false;
		}
	}
	
	return $value;
}
add_filter("pmpro_registration_checks", "my_pmpro_registration_checks");

//swap the expiration text if the user has used the trial
function my_pmpro_level_expiration_text($text, $level) {
	global $current_user, $wpdb;
	
	$trial_level_ids = my_pmpro_trial_level_ids();
	
	if($current_user->ID && in_array( $level->id, $trial_level_ids ) ) {
		//check if the current user has already used the trial level
		$already = get_user_meta($current_user->ID, "pmpro_trial_level_" . $level->id . "_used", true);
		
		//yup, don't let them checkout
		if($already) {
			$text = "You have already used up this trial membership. Please select a full membership to checkout.";
		}
	}
	
	return $text;
}
add_filter("pmpro_level_expiration_text", "my_pmpro_level_expiration_text", 10, 2);
?>