In fairness to everyone, swapping is encouraged. A deal can be struck to satisfy both parties. These meets are not a commercial venture but a melding of minds to help each other out.
Those who bring nothing or have nothing to share should expect to make offers or buy things of interest. why? Because the plants we keep often are rare (not available locally), algae/snail free and come from hobby tanks and not in random sale tanks from the LFS. You are also getting the benefit of direct pickup with shipping fees waived.
Personally i often get back what they give many times over. I am a humble hobbyist but make an effort to pack and distribute what i can to save livestock and educate on how to keep their plants and shrimp happy and living. I hope this practice inspires others to do the same.
If anyone has concerns about this, please pm me.