e.g. Two parties made an agreement that the products will be delivered on Apr 5th, but after the negotiation, the seller change the delivery date to March 29th. The seller only shift the delivery date 6 days earlier, so you may think it’s no big deal. However, this will be possibly used by the seller. They will say “we deliver the products one month earlier”, which benefits the buyer, so we hope that the sellers will pay the down payment more. This is a trap, freshmen can hardly notice it.