Is it possible to create a reseller account with cPanel that can resell reseller accounts? Also, how do you enable/disable overselling?

In WHM the reseller center can disable/enable overselling on bandwidth and disk space.

A reseller account that can sell reseller account would be called a power-reseller, you would need a special software to do this. I strongly recommend not to do this.

With Rvskins...you have the reseller be able to create sub-reseller accounts for cpanel customers. I don't really know how well it works since I have never tried it but it is in the RVskins admin.

Here is the info on it in rvskins since I don't really think I explained it correctly.

Sub Reseller System is designed for Resellers who want to allow users to manage multiple cPanel accounts without WHM access. Giving the possibility for reseller to sell multiple cPanel accounts in a single hosting package. Selling Multi-Domains using cPanel Addon domain feature doesn't satisfy users in some various ways especially it requires the same username and password to access cPanel and FTP. Think to the freelance web designer who works with a few companies. There are the need for multiple cPanel hosting accounts but don't want to pay for a reseller package which more expensive.