I didn't read the site posted, but other similar sites operate like this:

Since it's kinda like a collective of seeds, if everybody just wanted seeds from them, they would go out of business and have nothing to offer. That's why companies charge money for their seeds (duh). But where a company orders seeds, then sells them to you at a profit, this site just takes donations from people INSTEAD of ordering seeds. The $3 is just a charge to get the seeds to you and keep the site going. It's really just like trading seeds through the site, instead of directly through people.

In other sites, you can either send back the same type of seeds you ordered once you have made your own seeds, or more likely you can send in seeds you have from something else to contribute.

For example. Say that I have a shit load of tomato seeds, but I want some pepper seeds. Instead of me going to the store, paying $2 for a pack of seeds, this site will allow you to send in your tomato seeds and trade them for pepper seeds (while charging $1 for a service fee). This ensures that you pay less for the seeds you want, while at the same time keeping the site going, and the list of available seeds growing and available for everyone else.

Thanks WWBD, that clears it up.

So has anyone traded seeds with the place?