Ill. Admin. Code tit. 86 § 130.450
Where the seller engages in the business of selling tangible personal property at retail, and such tangible personal property is installed or altered for the purchaser by the seller (or some other special service is performed for the purchaser by the seller with respect to such property), the gross receipts of the seller on account of his charges for such installation, alteration or other special service must be included in the receipts by which his Retailers' Occupation Tax liability is measured, if such installation, alteration or other special service charges are included in the selling price of the tangible personal property which is sold. This is true whether the charge for the property which is sold and the charge for installation, alteration or other special services are billed by the seller to his customers as separate items (except when the purchaser signs an itemized invoice so as to make it a contract reflecting the intention of both the seller and the purchaser), or whether both items are included in a single billed price.
On the other hand, where the seller and the buyer agree upon the installation, alteration or other special service charges separately from the selling price of the tangible personal property which is sold, then the receipts from the installation, alteration or other special service charge are not a part of the "selling price" of the tangible personal property which is sold, but instead such charge is a service charge, separately contracted for, and need not be included in the figure upon which the seller computes his Retailers' Occupation Tax liability.
For information concerning installations by real estate developers and construction contractors, see Section 130.1940 of this Part.
Ill. Admin. Code tit. 86, § 130.450
Amended at 5 Ill. Reg. 12794, effective November 2, 1981