This sounds like a headache in the making but ended up being one of the easiest projects I’ve ever completed. The client purchased 4 different franchises with 50 total locations and wanted to merge them under one new brand. This meant we had to update their GMB listings and make sure that each GMB listing had a location page with accurate information.
Validate, Validate, and Validate Some More!
Avoiding issues with projects like these come down to two things: organization and coordination. The most important thing an SEO can do in this situation is to compile all of the information they can find on business locations and have the client validate that all of the business information is correct. This database should include all of the current business information found in GMB and new columns that document any client changes. This includes new business names, addresses, phone numbers, appointment links, business descriptions, website links, etc.
After the client has validated that the correct business listings and new information is in your database, validate that you have access to all of the GMB listings needed.
A bulk update to the GMB listings is the quickest and easiest way to change business information. Export the bulk edit template and then update the spreadsheet with the new information. Import the spreadsheet into GMB and the changes should be accepted almost immediately!
Compare the updated GMB listings to the business information on the actual website. Make notes of anything that needs to be updated on the website or GMB and report to the client.