There is an old saying that says "show me a good loser, and I'll show you a loser". That saying may be true in sports but not in business. No one likes to lose business, however, it happens to everyone and if you can be a good loser, it could make you a winner down the road.
When you lose a deal, rule #1 is not to burn any bridges. By going off on someone or slamming your competition (whom they have decided is better than you), you have nothing to gain. The distorted pleasure of slamming someone will be short lived and the pain of your angry actions could linger for years.
Rule #2 is put them on your mailing list. Chances are, that person will need a mortgage again some day and if you lose gracefully and stay in touch with them, you may generate future business and regerrals from them after all.
Also, remember the lender they originally chose may have done a lousy job, especially if the person shopped several lenders. If so they probably wound up like most borrowers who talk to too many lenders. They chose the one who promised too much because they didn't know any better and they unknowingly set themselves up to be disappointed.
So don't give up just because you lost a battle. The war is still out there to be won!