I hate it when I don't have all the requirements or they are fuzzy and I'm asked to estimate the task/project.

what, you don't like constantly redoing something that is working and adequate in every iteration, all because they didn't feel like committing to something specific the first time around?

Haha yeah, I try to be more firm on getting specific requirements now, but every now and then they still end up a little fuzzy. It sucks.

Have them sign-off on the requirements.

No matter how descriptive you are, there will always be a "but this is supposed to work like this" moment.

Having the client sign off on requirements as well as on achieved milestones is a key task that should not be omitted. With this the client will have a rethink when he/she or they are considering changing the project flow/scope.