Unless otherwise indicated, all addons fall under the following license:
Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License
A quick summary:
You can sell addons you've created, but do not sell add-ons which are not wholly yours, or you've gotten community input on. That's in bad taste, and is not good! You can however charge to setup an install, and customize. If add-ons are included in that 'customization', ask the addon author first and get their permission for being able to include their customization in your service. Remember the license is non-commercial and can only be waived with express permission of the author.
So to recap
You can sell addons you've created
You didn't create it - you can't sell it
If you want to include it in a package you're selling, you must get permission from the author. This includes any 'service' fees (for installation, updates, etc)
So please, follow the rules and don't be a chump!