I received several estimates to replace my asphalt shingle roof system and the prices vary greatly, Why?

If one estimate seems much lower than the others and it sounds too good to be true, it probably is. Many fly-by-night contractors’ below-cost bids seem attractive, but these contractors often are uninsured and perform substandard work. If an estimate is confusing, ask the contractor to break down the estimate into items/terms you can understand.