Don't pass counterfeit bills. Don't pass and possess counterfeit bills each of which contains the same serial number. And, for goodness sake, don't pass counterfeit bills to pay your motel bill while you're still there, at least if there's stuff in the motel room you'd like to hide.
Because passing the counterfeit bills to pay for your room may eliminate your reasonable expectation of privacy and justifies a warrantless entry by the police.
P.S. - Here, that principle doesn't apply, since unwittingly passing a counterfeit bill (which is all the evidence here allegedly showed) isn't good enough, especially when the motel isn't actually trying to boot you for it. We all do that all the time. Still: Be forewarned. I want you to be the best counterfeiter you can be.