About flags:
I should have the right to decline a flag :) It would be very rare that I would decline but if the flag makes me weaker for the position that I am fighting for, I might accept it only after taking a few lands.
About vflags:
If I (say blue) flag to somebody (say red) and red flags to somebody else (say brown), and if I did not flag brown, then I believe that I should be able to fight brown 1 on 1 provided that red has the middle position.
About truces:
I don't like truces. Actually, I don't like multiple versus one, truce is, by nature, multiple v one.
About flags vs truces:
Flag is a flag, if the player you are flagging to is losing the battle you should not feel obligated to help him. If you do, then it is a multiple v one and it gets hard to distinguish if the relationship is a flag or a truce. Exactly for this reason, in the above scenario, if red does not allow me to fight brown 1 on 1, I would start suspecting a truce (or even pga). There are so many players out there who believe that flagging should be transitive (scenario: blue automatically flags brown) but I see problems with it as I just explained.