Unverified, or claimed by someone else
An unverified profile loses map pack visibility, and you often can't tell from the outside. It's worse when someone else controls it, like a previous web designer, an agency you've left, or a listing Google created that you never claimed.
The wrong primary category
The primary category matters more than any other field. A plumber listed as "handyman" won't show up for plumbing searches, and "electrician" and "electrical installation service" rank for different things. It's also the field most often picked once, at setup, and never looked at again.
Service areas that don't match where you work
If you travel to customers rather than seeing them at a premises, the service areas you list affect where you appear. A profile that only lists Swansea won't do much for you in Gorseinon or Llanelli.
Hours, holidays and the details Google trusts
Out-of-date opening hours, no holiday hours, no services or products listed, three photos from 2019. None of these matters much on its own, but together they make the listing look neglected, to Google and to customers.
Name, address and phone that don't match
Your name, address and phone number written differently on Yell, Checkatrade, Facebook and your own site. Google checks your listing against the rest of the web, and differences weaken it.