[Marketpress] Product images blurry but ok when zoomed

Hi. Using Marketpress, I find all of the product images look fuzzy until they are clicked to see full size, then they have perfect definition. Have a look at https://fabhappy.com/gloriawhiting/store/products/peacock-feather-vase/ as an example. The vase looks fuzzy on the standard page and, if you click on it, the full size image is perfect. I tried it in a staging site with a different theme - see https://fabhappy2.wpengine.com/gloriawhiting/store/products/peacock-feather-vase/ - and it's the same. I'm worried that people see the fuzzy images first and get a bad impression of my site. Do you have any suggestions about how I can get the initial images looking sharper? Many Thanks - Peter.