Honestly, it's not false advertising. They agreed to sell for the advertised price. They want to impose a condition, which the buyer doesn't want to agree to. It's a private business, so they are not compelled to do business with the buyer if they don't want to.
It's a stupid practice, but they guy is trying to protect himself against bait-and-switch accusations. He's trying to offer the customer a solution that is mutually beneficial; the customer gets the car they want at the price they want, the seller tries to stay within the letter of the law and not bait-and-switch people.
I understand why this is off-putting, but at the end of the day all you can do is not give them your business. 6 on your side is going to laugh at you.
If you want the car and are fine waiting, do business with the guy. If you want to take a stand against what you perceive to be unethical or wrong, you can not do business with them. Beyond that, there's no recourse beyond leaving really angry Yelp reviews.
EDIT: I'm not defending this way of doing business, it's shady and stupid. But I firmly believe in a free market and that speaking with your wallet is the only way to do things.