Welcome aboard, Solaire. I've been on the site a while, but have only started trading in the last few months. I had some of the same concerns at first, but decided to trust those reputation stats. While some would not trade with me because of my (then) non-existent rating, others gave me a shot, typically asking that I send first. It has been a great experience.
To protect yourself, be consider paying for delivery confirmation with all but the smallest value trades. If the intended recipient of your cards ever claims you did not send, a delivery confirmation number (DCN) will provide proof of delivery. Delivery confirmation adds to your shipping costs, but it is the least expensive way to prove you shipped and that the recipient received. If you have (or will set up) a PayPal account, you can purchase and print postage from them, and it includes free delivery confirmation. See http://www.paypal.com/us/cgi-bin/webscr?cmd=_ship-now if interested.
If offering cards for cash, require users send money via PayPal, or some other agreed upon means. Make sure you understand any fees or limits on using PayPal, so you don't end up short, and make sure the associated amount takes into account any fees or charges. If accepting checks, be sure to have them send first, and have a two-week delay established as part of the terms of the trade, so there is time enough to be sure the check will clear the bank. You ship only after two weeks have passed (not when the deposited check is credited to your account).
There are some good posts out there on shipping cards. Be sure to review those.
Speaking of reviewing things, be sure to visit the profile of each potential trader before you offer a trade. Many include information or criteria that may affect your trade (or their willingness to trade).
Best of luck to you, and I hope we'll be able to trade with each other soon.
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TradelistBlack and Blue--not just for bruises anymore.