I just tell them they lost the bid. If they want my business they should have given me the vehicle at the price I bought it less a substantial amount as I do not need them to copy the deal, they have to beat it. It stops the calls.
They may remember me the next year or two later if I am actually shopping for a car and treat me better. It may help other buyers get a better deal if they know there are people like me who do their due diligence before plunking down their money.
If a dealer gives me a low ball I go back and ask for the deal. If they do not honor it, I tell them nice try, I would not buy anything here, not even service as you cannot be trusted.
I have been told by friends that sell cars that I am a salesperson's nightmare. They have quotas and managers. If you hit them at the right time of the month they can give you deals that are rare.