The product image is cropped or blurry

WooThumbs uses the  Single Product Image size from your WooCommerce settings. This can be accessed at WooCommerce > Settings > Products > Display > Product Images. Some themes disable these options, so you'll need to contact them in order to gain access.

Here you can set a width, height, and whether to crop the image.

Usually, it’s best to set the width relative to your theme’s display area, and then set the height to something like “9999” with  Hard Crop? unchecked.

Once you change your setting, you will need to  regenerate your thumbnails.

If you are using WooThumbs, you will also need to clear your image cache. Go to WooCommerce > WooThumbs and click Clear Image Cache.