If I understand correctly based on some clarifications in the comments, you are the seller of services. Some people buy services directly from you, others buy services from some other company and that company then employs you for part or all of the work:
1: (person A asks you to do work) -> (you do work) -> (person A pays you directly)
2: (person A asks company X to do work) -> (company X asks you to do work) -> (you do work) -> (company X pays you) -> (person A pays company X)
From your perspective, person A would be the end-user in both scenarios.
In scenario 1, person A is also the client, and you are the vendor or the contractor.
In scenario 2, Company X is your client, and they are a reseller or distributor of your services; you are a subcontractor. (Company X is the vendor or contractor from Person A's viewpoint.) You may still work with the end-user directly on your portion of the job, or you may work entirely through your contacts at Company X.