I'm working on a project where our dev team gets the specifications from the business part of the company. Both the business management and the IT management require estimates and deadline projections, as they should.

The good thing is that estimates are mostly made by the actual developers who get to do the required features. The bad thing is that the specifications are usually either too simple (it turns out you're left with a lot of question marks over your head because a lot of information seems to be missing) or too complex(up to the point that you can't even visualize where everything would "fit" in the app). More often than not, the business part of the specs are either incomplete or unaware of what can and can't be done (given the previously implemented business logic).

Dev team is given about a day per new spec to give an estimate and we do try to clear uncertainties, usually by meeting up with whoever did the spec. Most of the times it turns out that spec writers haven't really thought everything through, and it's usually only when we start designing and developing that we end up in trouble, as a lot of the spec seems to have holes.

How do you deal with this? Are you generous on estimates in advance?