There is no magic number, and anyone who gives you one is guessing. The useful question is relative. Search the service and town you care about, open the map pack, and write down the review count and rating for the three businesses showing up. That is your target. In a small town it might be forty reviews. In a metro it might be four hundred. Either way, you now have a real number instead of a goal somebody invented in a sales call.
Velocity matters as much as total. A profile with three hundred reviews and nothing new in a year looks stale next to one adding eight a month. Build the ask into the job instead of running campaigns. The tech asks at the end of the call while the customer is happy, you follow up by text the same day with the direct review link, and the office checks the list weekly. Four to ten a month, every month, gets you there and keeps you there.
Never buy reviews or run incentives. Google filters obvious batches, competitors report them, and a review purge can take your real ones with it. Also stop worrying about the occasional one star. A perfect five with sixty reviews reads fake to customers. What you want is a strong average, recent dates, reviews that mention the actual service and town, and your own reply under every negative one showing how you handled it. That reply gets read more than the complaint.
Send the site over. We will tell you what is broken, what you could rank for, and whether AI search knows you exist. No charge and no pitch deck.