BC currently offers a button to create bookings, even if there are no slots left. That link should not be available at all, if a booking is not possible.
The renderer currently does not indicate if the current user has already booked an instance. The one-click Ajax though has a nice feedback text on the button for existing bookings. The static renderer should do the same.
Proposed resolution
Render a link if booking is impossible
Statically render "Booked" on instance buttons with existing bookings