When several businesses have identical service categories, Google Maps does not rank them simply by category. It primarily considers relevance, distance, and prominence to determine which business is the best match for the specific search.
For example, two plumbers may use the same category, but one can appear higher because it is closer to the searcher, has stronger prominence, more reviews, or better supporting business information. Google also considers the overall context of the search, so the same businesses may rank differently depending on where the customer is searching from.
So, having the same service category does not create an equal ranking position. Keep your Business Profile complete and accurate, build genuine reviews, and make sure your services and business information clearly match what customers are searching for.