Google has confirmed that review count, review score and review text all contribute to how businesses are ranked in local results. They also affect the click: two businesses side by side in the map pack rarely split traffic evenly when one has 12 reviews and the other has 180.
The lever you control is volume and recency — asking every customer, consistently, and replying to what comes back. What you cannot control, and should not try to, is which customers get asked. Screening for happy customers first breaches Google’s policies and risks the profile that the rest of your local visibility sits on.