What percentage less can I expect to pay for a used vehicle when I pay cash?

None when buying from a dealer. They may actually want more if they know you are not financing. Get the price in writing first before you tell them you are paying cash.

I tend to disagree, you're the buyer, you have cash money, you're in control. If they don't want to deal with you, they watch you and your cash walk out the door! Remember, YOU are in control.

It is a sellers market now. Cash means nothing at all these days unless you can find a tax cheat who will pocket the cash and not pay the taxes.