New folks, until they have a few posts under their belt or have a veteran vouch for them, are expected to execute their end of the transaction first until you gain the confidence/trust of some of the members.
You can get an idea of how trustworthy a Geek is by viewing their feedback.
As noted above, it's best to post what you're willing to trade and what you're looking for in trade. Some Geeks use the Virtual Humidor for this and set up a humidor that can be easily viewed by others.