Selling Zencart Store including Contributions.

Hi,
I am new to this forum and just wanted to ask a question.

Is it legal for a company to commercially sell a zencart store full of products as a business opportunity with the actual store complete with all built in contributions that third parties have coded?

You could sell a store with products that uses Zen Cart as a business opportunity whether it is trading or not. You cannot "sell" the Zen Cart software, but the new owner would be free to use it. You should note also the license requirement to display prominent notices in any files that you change.

Contributions downloaded from this forum can be treated in the same way as Zen Cart. There are however some contributions available from third party sites, sometimes paid for, sometime not, which may be operating under different licenses and these would have to be checked individually if you are using them.

Before going further though, I'd recommend that you read the GNU General Public License distributed with Zen Cart. It's designed to be as simple to understand as a license can be.