eBay allows you to test your listings on the sandbox website. For sending items to eBay sandbox you need to have a separate eBay account. Your existing eBay account can’t be used for the sandbox website.
Sandbox address: https://sandbox.ebay.com
Link for a new account registration — http://developer.ebay.com/DevZone/sandboxuser/
After registering an eBay sandbox account, you will be able to connect this account to Salestio. A sandbox account can be added the same way as a regular live account. The only difference is that you should select the 'Sandbox' mode on the 'Add eBay account' page.