- make sure that in the reviews there are also some keywords (for white-hat approach, ask your customers to mention what service they've bought from you, as usually the provided service is also the keyword, otherwise go with black-hat and buy them putting natural looking keywords into the review). As usual, not spam them and make them look realistic and natural too.
- do NAP citations and mentions (try having from 50 to 100 nap citations, you can usually buy them for relatively cheap),
- use secondary categories for your gmb (if your main category is "pastry shop", for example, add some other relevant categories such as "cupcakes", "sweets shop" and stuff like that), searching on google you can find lists of all the possible categories, so you can search if there are some similar (usually when you add categories on GMB it will suggest some categories too)
- post photos, videos, and other stuff, try adding them directly from the place where your business is located with GPS on, and also check this thread that talks about this with a twist
https://www.blackhatworld.com/seo/ranking-local-gmb-tip.1308771/.
This stuff still works
- I've read many saying that CTR manipulation works with GMB, but I haven't used that a lot, so I can't give you advice on that because I'm not very skilled in this
This is all that comes to mind at the moment. I can suggest you to look into Chris Palmer SEO and Semantic Mastery on Youtube if you want to dive deep into that stuff, I've learned lots of stuff from them and they really have some solid ideas.
