Not sure how tigerfree is being marked as scammer. I bought two of the raspberry pi units previously, they showed up NIB from Amazon if I remember correctly. If in doubt, feel free to use escrow, but I'd buy again from tigerfree if I needed more.
Have you read the feedback on his account? People suspect he's purchasing the goods illegally (with stolen credit cards or some other method like that) from sites like Amazon, and shipping them directly to customers. Sounds similar to the trade he did with you, since the Pis came directly from Amazon, and not from tigerfree.