You may check the "Price Excludes" part on the tour page. 

The optional activity fee and tour guide tips needs to be paid in cash. Optional activities are always recommended and will have to be paid in cash to the tour guide if desired to take them. Tour guide will arrange tickets for all customers in the group tour. On the other hand tips are not optional; this is a mandatory fee that also needs to be paid in cash when on tour.  Passengers can not buy their own tickets as the tour guide will have the ticket ready for you.