Velocity matters more than the historical total: a steady trickle reads as a living business, while two hundred reviews in a fortnight reads as manipulation and often is. Responses matter too — publicly and calmly answering a negative review is more persuasive to a reader than a page of five-star ratings.
Never incentivise reviews in a way that breaches platform policy. Removal of an entire review set is a real and common outcome, and it takes the good ones with it. Asking every customer at the right moment, with a link that works on a phone, produces more reviews than any incentive.