Google is testing bookings using Google Duplex, but I have yet to see how it looks as a user when they use Google search to book a reservation. Thibault Adda shared screen shots of this being tests on an Olive Garden in Florida. He shared the screen shots on Twitter.
You can see the buttons for reserve a table and tables tomorrow:
Then when you click it it says "The Google Assistant will call the restaurant to request your reservation" It asks you to select the date, number of guests, preferred time and if that time is not available, to ask for other times.
Pretty cool stuff! I cannot replicate this, I've tried for this query.
Forum discussion at Twitter.
