Materials vendor
In short
The supplier a contractor buys from. Not a defined tax term — but on an MRRA project the vendor, not the contractor, is often the party actually taxed.
In full
Materials vendor is a descriptive term rather than a statutory one. The vendor is a retailer, taxed under the retail classification on the sale.
The vendor matters to a contractor because of who is taxed on materials. On an MRRA project the tax attaches to materials rather than to the contract. A contractor who pays the vendor at the register has satisfied that obligation, and the vendor is the party who reports and remits it. A contractor who instead gives the vendor an exemption certificate and buys exempt takes the obligation on, and later remits an amount equal to retail transaction privilege tax on the cost of the materials.
Which certificate a vendor may accept depends on the buyer. A licensed contractor presents Form 5000. An unlicensed contractor cannot complete a Form 5000 properly, having no license number to put on it, and uses Form 5000M for a statutorily exempt purchase, or an approved Form 5009L on a Modification project where the prime has obtained one from ADOR. Form 5005 alone is not an exemption certificate and a vendor should not accept it as one. ADOR's Contracting FAQs describe a Form 5000M presented together with a Form 5005 as the route for an unlicensed contractor on a one-off Modification project; Form 5000M states that it pertains only to maintenance, repair, replacement or alteration projects. Published sources differ, and a vendor relying on the pair on a Modification project is relying on a certificate that excludes the transaction on its face.
A properly completed certificate may be accepted in good faith and retained as the record of why the sale was exempt. An incomplete one may not.
A.R.S. §§ 42-5061(A), 42-5008.01; ADOR Contracting FAQs, Retailers and Exemption Certificates