I recently started writing for a firm, and this is my first post.
I will state that the more specialized your topic the harder it is to find people qualified to take the work... wouldn't you rather the work was declined than to take your money and provide subpar work?
At least for the site I write for, I seem to have observed that there is a bit of a shortage in one particular concentration... Fortunately for me, it is within my area... but as a new writer I am limited in how many assignments I can accept in a single day. This probationary limitation is good business, and if all the current writers are occupied that is unfortunate.
Don't view a site as a scam simply due to the fact that there was not someone to take the assignment... they might have lacked someone with the appropriate expertise, those writers had a full plate, or were away for the time being.
I teach on Tuesdays and Thursdays... if someone needs some international economics or finance help for immediate turn... I am lecturing and can't help.
Best of luck in the future... if you got your money back, then it is not necessarily a scam!
Also... Did you post a clear description of the assignment? Did you also post the necessary supplemental material?
So far, I have noticed a great many assignments are posted without sufficient information for writers/researchers to accept the job.
Particularly for statistical analysis assignments!