This is indeed a very valid question which we take at heart at IntroNiche.

It boils down to common sense.
We strongly recommend that you:

• only deal with people you feel comfortable with
• never give anyone access or insights in your clients database

Introniche allows for cooperative marketing, not database exchange.

This means that when you make a deal on Introniche, you agree that you will promote the other party to your selected client database in return for a similar service. 

This means that you will not have to give the other party access to your database.

In case you need to verify each other's database prior to making a cooperative marketing deal, we recommend you use a certified and neutral third party like an escrow service.

For email database, we recommend you have a look at the Direct Marketing Association or these articles on the BeRelevant blog.