If you ever need to verify they’re certified to hold out the work they’re booked for, you'll be able to ask to see their ID. https://wiki.lvl1.org/index.php?title=%2Fwww.northwestu.edu%2F%3FURL%3Dhttps%3A%2F%2Fchingfordplumber.co.uk&action=edit&printable=yes