Jay, I searched "real estate transfer fee" in Wis Statutes and found this, among others that weren't relevent. This states that it is the Grantor's (seller's) responsibility to pay the fee
77.22 Imposition of real estate transfer fee .
77.22(1)
(1) There is imposed on the grantor of real estate a real estate transfer fee at the rate of 30 cents for each $100 of value or fraction thereof on every conveyance not exempted or excluded under this subchapter. Blah, blah, blah!
This supports the above by stating any excess or shortage in the fee will be charged or refunded to the grantor.
77.26(2)
(2) If the department of revenue determines that the amount of the real estate transfer fee reported was in error or that an exemption was improperly claimed, the department shall compute the additional transfer fee to be paid by, or the amount of the overpayment of transfer fee to be refunded to, the grantor.
http://www.legis.state.wi.us/statutes/Stat0077.pdf