[jacquesm]

Never ever agree to anything at all under pressure. If that's what it takes for the offering party they are either incompetent or malicious there is no pay-off in finding out which. That goes for hiring offers but also for any other kind of offer.

The one exception I can think of for exploding offers is if a key employee has left and the company will lose direction if the position isn't filled immediately. This normally is not the case in start-ups.