Wis. Stat. § 133.05
Competitive injury is a required element under this section, but intent to injure is not. OB-GYN Assoc. of Neenah v. Landig, 129 Wis. 2d 362, 384 N.W.2d 719 (Ct. App. 1986). A violation of sub. (1) occurs when a discount, both secret and unearned, tends to injure or injures competition. "Earned" discount is defined. Jauquet Lumber v. Kolbe & Kolbe Millwork, 164 Wis. 2d 689, 476 N.W.2d 305 (Ct. App. 1991). This section is not unconstitutionally vague. Knowledge is an element of a violation of sub. (2). Carlson & Erickson v. Lampert Yards, 183 Wis. 2d 220, 515 N.W.2d 305 (Ct. App. 1994). Civil violations of this section must meet the ordinary civil burden of proof. Carlson & Erickson v. Lampert Yards, 190 Wis. 2d 650, 529 N.W.2d 905 (1995). "Rebates," "refunds," and "discounts" in sub. (1) mean essentially the same thing, a reduction or credit that is tied to the price of the good or service being purchased by the recipient of the reduction or credit. To be a "discount" a payment or allowance must be a reduction from the price that would be paid if the "discount" were not given. Tele-Port, Inc. v. Ameritech Mobile Communications, Inc. 2001 WI App 261, 248 Wis. 2d 846, 637 N.W.2d 782, 00-2627. Civil violations of this section must be proved by clear, satisfactory and convincing evidence.