We did Gray Line tours on the US side. It was your "average" tour with a long stop in one souvenir store (over-priced) and instructions from the beginning not to shop anywhere else.
I agree with Fern, I usually tip about $5 per person for a tour, never a percentage.
I will definitely tip more to a guide and/or driver who diverts the bus to take us somewhere special. Red October got BIG tip from us because they took us away from the tourist shopping areas to buy Caviar, and RO has their OWN souvenir market (we bought enough there as well).
As to that guy who sits next to the driver, I always figured he was just getting a ride to work.