Multiple GMB Listings for Service Based Business?

I am working on a friends business. Hypothetical business - they are a cleaning company.

They don't have a physical location, they service customers by visiting their homes and cleaning them.

I have noticed a large, national franchise competitor has one domain with a location page dedicated to each city they service. domain.com/city1 , domain.com/city2 etc

This competitor also has separate GMB listings

Brand Name Cleaning Service City 1
Brand Name Cleaning Service City 2
etc

It looks like individuals pay for the franchise, and then they run that area. Each GMB has its own reviews, and the profile picture is a photo of the cleaner that covers that area.

My friends business isn't a national franchise, however they do cover multiple cities and areas across the region.

They currently have a few pages domain.com/city1 domain.com/city2 etc but only have one GMB listing.

I am thinking of building out individual GMB listings for each, and linking each to the relevant city page.

So for example domain.com/city1 would have its own GMB listing "Brand Name Cleaning Service City1" , then do this for all major cities, creating unique landing pages with unique content on each.

Would this be the best strategy to create unique GMB listings for each city, as opposed to just relying on one main GMB listing - or should I just stick to the one and optimise the city pages on site?

How the thing going? A GBM listing without physic location could be suspend anytime. Should be creating Service Are Business without address in each city.

This is a local SEO technique. For example, there's a local web design company with a real office in my city, but they also have GMB listings in every city nearby, including rural townships. But the Google street view just returns a regular-looking home for all those listings.

Either they are paying those local homeowners to help verify their locations or they will get pinched by Google soon enough.