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BadMoon - It appears you got the deal you wanted, if the salesperson irked you that much, can you switch to another sales associate at the same dealer to seal the deal? It would appear that you could explain to the current salesperson that based on the phone message, you would prefer to finalize the deal with someone else; with the understanding that you will not go to the GM about the phone message. All the other prior negotiated items (trade-ins, add-ons, etc.) were approved by a sales manager, so it shouldn't be difficult.
You shouldn't reward bad behavior, and his lesson will be a lost commission for his mistake. This would hopefully avoid any quilt you may have about getting someone fired if you did go to the GM.
Best of luck with your purchase. BTW, my advice is to install carseat protection mats prior to installing your child seats. My kids love using the rear seats as a step getting into their booster seats. Should save wear and tear (and dirt) on your rear seats.