Thanking you,
hari
There are basically four levels of AdWords users:
1. Resellers. These are companies selling AdWords on behalf of Google. At present, there is only one reseller of AdWords that I'm aware of, Bellsouth [webmasterworld.com]. This deal is based on Guaranteed Clicks [webmasterworld.com].
2. Affiliates. These are people who receive a commission when someone signs up with AdSense or AdWords through their affiliate link or channel.
3. Agencies. These are companies who represent clients and serve as the middle man between AdWords and Clients.
4. Individual Users. This group logs directly into their accounts (and sometimes through an MCC), and handles the advertising themself.
Of course, you also have agency resellers and affiliates as well, making the possible levels of how certain relationships are handled a bit more convoluted.