Sub-roles and role purchase
I think you are looking for something like Sub Users module to set relation between two user types.

I also sell membership with help of Drupal Commerce in D7 &amp; I have used same thing but some modified version of the module which you can find at my given link here --

https://drupal.org/node/2049703

I sell membership to have some access &amp; sometimes I create a usertype who has got authority to create more sub user under him to have access allowed for that particular membership type.