Avoid purchasing certain products without them becoming out-of-stock

disable-purchasing-instock-products.php

<?php


/**
 * @param $query
 * @param $product_id
 * @param $exclude_order_id
 *
 * @return mixed|string
 */
function ywp_prevent_purchase_products( $query, $product_id, $exclude_order_id ) {
	$bad_products = array( 5544 );

	if ( in_array( $product_id, $bad_products ) ) {
		$stock = (int) get_post_meta( $product_id, '_stock', true );

		return "SELECT $stock;";
	}

	return $query;
}

add_filter ( 'woocommerce_query_for_reserved_stock', 'ywp_prevent_purchase_products', 10, 3 );