What practices make you say, "I can't believe anyone is still doing that!"
Dealers who tell customers: "We can't get you financed unless you buy that $1,500 extended warranty." Or GAP or etch or whatever.
Dealers who tell customers: "You don't qualify for credit, but we can get you financed if your wife (or husband) signs with you."
Dealers who tell customers: "Oh, that's our Internet price for the car. It's for good credit customers. Your credit's lousy, so you'll need to pay more for the car."
Lenders ask for co-signers all the time, don't they?
Those facts describe a slam-dunk [Equal Credit Opportunity Act] Reg. B violation. A creditor may ask for a guarantor or co-signer if the applicant's credit is weak but cannot ask that a spouse be the guarantor or co-signer.
What's wrong with saying, "Your credit's lousy, you'll need to pay more for the car?"
Any difference between the car price for a good credit customer and a bad credit customer is a finance charge, for federal purposes and probably for state law purposes as well.
So the right answer should be what? "Your credit's lousy, you'll need to pay a higher interest rate for the car, but the price is still the price we quoted in our advertising?"
Your last sentence is the right answer.
Do you worry about criticizing clients -- or potential clients -- in print?
If they're violating the law, I don't have a problem criticizing them.