Well… until you enter into a purchase agreement, and lock your mortgage rate, there is no guarantee you will be provided the rate quoted. This is listed in the fine print, but may have not sunk in.
For example, you agree to a longer escrow period and closing is set for 80 days out. This will require the lender lock the loan with a 90 day rate lock (done in 15 day intervals), which will be worse pricing than a 30 day rate lock.