Is there any disadvantage in taking all quests you are offered?

[Boar]

If you take the quest from the ruler who asks you to kill the ghost (in Verlon Forest?) and you decide not to do it, you will have a failed quest on your record. Similarly the ruler who asks you to make a treaty with the barbarians, and once you complete it asks you again -- if you take the quest it will fail. Several quests ask you to kill off someone, and if they have a shop that shop will be closed to you. Personally I look at the shop first, and if I decide that at, say, level 23 I'm not about to buy any werewolf elves and don't want ent sprouts that are at some shop -- or whatever is fairly worthless, I'll go ahead and kill them and get the experience points.