Kate, from what I understand you can use this thread for asking the person where your money/item is. So for instance your post might look something like this:
"MSK, just wondering where my Ju-Ju-Be Diaper changing pad is that you forgot to send with my bag. You told me you would ship it out, and I haven't received it yet. Can you please contact me via PM, or by email at email@example.com
as soon as possible? Thanks so much!"
Nice, but effective way of letting the forum know there is an issue with a particular member. You can then always come back and delete your post, or report the post and let a mod delete it for you.
FWIW, I have used this forum to do this exact same thing with a member that didn't follow through with their side of a transaction.