Three things you need to know about good faith estimates.
As far as the interest rate, you’re always working with a moving target. If you’ve got one or several from a week ago you’re comparing, it’s old news. Unless you’ve specifically agreed with the loan officer who sent it to you, it’s not locked and quite likely has changed. Constantly chasing the lowest rate is like a dog chasing its tail – you’ve got to stop at some point or you’re going to fall down.
Second, make sure the estimate you get has a bottom line and it all adds up. Your payoff plus your closing costs need to total the amount of the new loan. If they don’t you’re going to either come to closing with a chunk of money or raise the loan amount thus distorting the payment amount you’re looking at.
Last and most important, the estimate is worth the integrity of the person preparing it. If you don’t know them, you don’t know the validity or the accuracy of what you’re receiving.