yeah but if it doesnt reach the tier i want, and i back out, and if others do the same as me, then someone who didnt want say a 150 tier only 100 tier, people like me backing out jeopardizes the people who are content with the lower tiers
Yes, but if we look at it your way, only 100 people order but 60 people are tempted to order if it hits 150 sets but it would never hit it because of the 60 people that didn't sign up. If you have a realistic tier amount then it's fine, if we don't hit it I really doubt that many would cancel.
You have a chance to cancel near the end of the GB so then the GB organizer can re-evaluate the situation to see what to do next, I mean if your expectation is 500 sets then I'm pretty sure we won't hit it.
In all situtations its better to order first then back out later, you can even tell your GB organizer that if it doesn't reach X amount I might back out that way everyone knows, its a lot easier to do that then go if we hit X amount so and so will go in and if we hit Y amount these other people will join