I see no problem with having a B team equal in
strength to the A team. If a decent team decides that two
teams making the playoffs is better than one team
having an outside shot at winning it all, that is the
coach's decision.
As for flip-flopping A and B
teams, having small RR brackets of 4-5 teams is part of
the problem. If you can guarantee multiple strong
teams of equal strength in each bracket, it is less
likely to occur.
As for playing, I see no problem
with putting in a weak team. The coach shouldn't be
upset about a team playing to it's level. Most of the
times, these kids are enthusiastic and on their own as
the coach accompanies the A team. As a tournament
staffer, I see it as my duty to foster this enthusiasm. I
have only seen one coach become truly upset about any
of his teams, A or B or F or whatever, losing. I
think I would be very upset to see any coach direct
his/her annoyance towards a B team for losing.