He tried id=3 . Nothing.
The query inurl:index.php?id=1 shop is specifically used as a to find websites with a certain URL structure. Security researchers use these "features" of the URL to identify potential vulnerabilities. Functional Feature: Dynamic Content Retrieval inurl index php id 1 shop
Malicious actors use such dorks to build target lists. Combining inurl:index.php?id=1&shop= with site:.com or intext:"cart total" helps enumerate vulnerable e-commerce sites. He tried id=3