S.D. Codified Laws § 58-17-59

Any person who provides health care and who waives the deductible or co-payment for more than one-fourth of his patients during any calendar year, excluding waivers under § 58-17-58, or who advertises that he will accept from any third-party payor, as payment in full for services rendered, the amount the third-party payor covers, is presumed to be waiving the deductible or co-payment as a regular business practice.