Don't assume anything when it comes to sourcing sites, most of these things like gold members and so on are paid for by the seller, it buys them instant credibility.
The site itself is like all other sourcing sites, it will have good companies and it will have scammers packed to the walls, so it is up to you to do research on every individual supplier you are interested in doing business with.
The reason you are getting slammed with emails is because you have posted a buying lead, and those emails won't stop. Every company that either supplies, knows of someone that supplies or even supplies something remotely related to the information in your buying lead, will be trying to promote their details to you.