What is overselling ?Overselling means that the system limits resellers via the resources that their cPanel accounts actually use instead of the resources that you allocate to them.
Overselling enabled ?
When you set resource limits for a reseller and enable overselling, a reseller can create accounts with resource limits that exceed the maximum amount that you allocate. After the total combined resources that all of the accounts use exceeds the reseller's resource limit, the reseller cannot create new accounts. However, their accounts can continue to use resources, up to their own allocated resource level. The resource limit does not affect an account's use of resources, only the reseller's ability to create more accounts.
Overselling disabled ?
If you disable overselling for a reseller, they can create accounts until they allocate the maximum amount of resources that you assign them. After the reseller allocates the maximum amount of resources that you assign them, they can no longer create accounts. The amount of disk space or bandwidth that the accounts use does not affect the reseller's ability to create accounts if you disable overselling.