Google seems to be testing showing the number of bookings that happened through a local services ads directly in the Google ads. Tom Waddington posted a screen shot that shows Google displaying "booked 870+ times near you."
Tom posted this screen shot on Twitter:
This is what I see:
I suspect showing the number of bookings does two things; (1) gives confidence to the shopper that the business is dependable and (2) encourages the business that doesn't show the number of bookings to use a Google backed booking system.
Forum discussion at Twitter.