Ads is my thinking also, either Google Ads or Google Local Service endorsement type ads.
There could be an issue with showing more variety or choices to people. If there are 5 on the map, it might mean fewer are clicking over to the Maps area and pounding the servers with more queries. It could lead to more Page 1 clicks, which would mean a happier end user.
It is quite some time ago, but i have seen a 4Pack by doing some queries for a customer. On the first place was an ad (marked) and on position 2 to 4 the usual results. That was only for a short period here in Switzerland.
New advertising option:
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