My first Prius, Toyota warned against putting a hitch on, even for a bike rack. And said it might void the warranty. Except they gave a towing capacity for the same car if sold in Europe.
I'm not sure if they gave up on that, but I don't intend to tow anything with the car anyway. I was thinking of making the hitch totally stealth, you can take the receiver part off so the dealer doesn't need to know about it. But I had to cut a hole out of a plastic panel so it's pretty obvious.