The job is:
List the product price for 1pcs. But you can specify in admin that it can only be sold as a carton with 12 pcs.
Note: Not done by Products Attributes.
Normal users can buy one product for a price of ex. 10$
Users can be added as a wholesaler and when they are logged in they can buy a carton with 12 pcs for wholesaler price ex. 75$
Setup shipping cost is 2,5% of total order.
I think this can be done in Table Rate module.
I just dont know how...