For ages I struggled with proportioning my Etsy photos so that they weren't accidentally cropped when I listed my items. Also, I wanted clean white backgrounds too.
Based on Adobe Photoshop / PS Elements, I created a PDF file in a kind of 'how-to' format and, if it helps, you can download it for free from my blog at www.what-lies-beneath.co.uk/?p=286. Remember to right-click on the link and select 'Save link as.....' - don't just click on the link.
Though its not by any means the definitive guide to the subject, it serves as a pointer and I know by some of the posts I read on this forum, its a problem for a number of Etsians......
Hope you may find it useful ;-)
Emms