I've been putting watermarks on my products and I guess that's all I can do. I'd added a couple listings and was searching around for more tags. I right-clicked on another shop owners prints and of course got the menu 'save image as'. I didn't but wondered how good quality a viewer would get if they just downloaded the thumbnail and then 'grew' it to 8x10. Following the etsy guidelines I think you could produce a pretty decent print. I don't know if saving as 80 dpi would make a difference or if etsy has some techno solution that "embeds" the thumb as a part of the larger page.
Any thoughts.