Thanks for contributing to our forum. In order to offer different sizes of the same piece of clothing in one listing, you will just need to create a variation listing, which is an option when creating fixed price listings in some categories - including most (if not all) clothing categories.
Once you have selected “Fixed Price” as your Sale Type and chosen a category for which eBay supports variations on the Auctiva lister page, you should see an “Add/Edit Variations” link just above the Second Category drop down menu which you can click to create your variations.
You may also want to review our tutorial which covers the creation of variation listings by clicking the following link: http://www.auctiva.com/help/tu...x?id=multi-variation
I hope this helps. If you need any further assistance with your account, please feel free to contact our Customer Support team by mousing over the “Help” tab and selecting the “File Support Case” option.