In plain terms
The category matters because of what it rules out. A service provider may not sell or share the information, may not retain or use it outside the direct business relationship, and may not combine it with data from other sources except as the contract allows. The definition sits at Cal. Civ. Code section 1798.140(ag), and the contract terms that keep a vendor inside the category are set out in the agency's regulations at 11 CCR section 7051. Miss those terms and the vendor counts as a third party instead, with different consequences for both sides.
What it means for a registered broker
Any tool that touches your deletion cycle processes personal information for you, so the addendum matters more than the feature list. Look for the specified business purpose written out rather than described generically, the prohibition on selling or sharing, deletion or return of data when the contract ends, subprocessor flow down, and terms covering custody of your DROP key. You remain the responsible business under CCPA. No vendor can take that on for you, and one that says it can is describing something the statute does not allow.