Can ambassadors use their own code and double dip?

Ambassadors can use their own code for commission. 

However, this usually isn't a problem, as long as you are profitable on every sale. 

There are two main reasons for this: 

1. Ambassadors buying your product is a good thing. They need it to take photos and share on social media, talk about it with friends, etc. The more products they buy, the more pictures they can take.

2. The money you earn is the same whether an ambassador uses their own code, or somebody else uses it. Your profit is the same.

If you really want to prevent this from happening, you can add a clause in your terms and then terminate ambassadors that do this (but this isn't recommended).