Teresa I'm sorry to hear you've been had before. It's always better to do small trades first and establish relationships with people before you go sending hundreds of dollars worth of plants to them. Once a relationship is built then more plants can be shared safely and with a better peace of mind.
That said most members have established names for themselves in the garden.org community so when in doubt go see how active they are on garden.org. If they don't post often or haven't been a member long proceed with caution. Also check to see what photos they've added, if they say they have 500 daylilies and 300 irises but never shared a photo of either once again proceed with caution. Of coarse not posting much or not uploading photos doesn't make a person a crook, but the more active a person is the more they have to loose. The chance of an established garden.org member cheating you is slim to none because they wouldn't want to ruin their reputation in the garden.org community and the respect of fellow members over a trade.
This is not a shot at any member or in anyway trying discourage trading. These are just words of wisdom from someone who has traded plant material with hundreds of people from all over, both on garden.org and abroad. Trading is a great way to acquire new plants for your garden and I'm all for it. It's honestly how I have most of the plants I have now. Gardening is all about sharing both plant material and knowledge with one another. Happy trading everyone and I hope you all get some plants you've been looking for. All my daylilies are too small to trade or I'd join in but if anyone wants to trade a few seeds please feel free to tree mail me.