This will help to restrict/block wholesale users from checkout. Create a custom role OR use an existing (e.g., subscriber).
add_action( 'woocommerce_checkout_process', function() {
if ( ! is_user_logged_in() ) return;
$user = wp_get_current_user();
if ( in_array( 'subscriber', $user->roles ) ) {
wc_add_notice( 'You are not allowed to checkout.', 'error' );
}
});
