Hi AmitP, thank you for your questions.
We're italians and so, for first, we did an add-on who integrates cscart 2.1.3 community with the italian site of eBay (www.ebay.it).
The API (and their XML formats) are lightly different from eBay.com, but a very few hours of development we can adapt them to interact with the american site.
We must only change the XML format of the requests & responses of the communication.
About the testing, at the moment we finished it internally. I sent an email to admins yesterday, but at the moment no one replied to me.
I'm waiting for their reply, to first presenting the product to them, and to start their session of tests.
Innoteam - The Content Partners
michele DOT amori AT innoteam DOT it