E-Commerce Services - enforcing non-competes

Looking at an online service business for sale which has a large overseas operations. One of the Sellers is a foreigner and one is American. I'm wondering how e-commerce deals typically enforce a non-compete. It seems like it would be very easy for the seller to maintain the customer and employee names and then start up under a different brand, and it's possible the Buyer wouldn't even know it's happening. It would then be nearly impossible to enforce any kind of non-compete in such a situation.

How do people in the e-commerce space guard against the ease of evading a non-compete?