One way to insert images that won't be supersized is to place them directly into the listing description.
When you are on the one-page lister creating an ad, click on the button in the toolbar of the Item Description editor box that looks like mountains and sunset (it will say "insert an Auctiva hosted image" when you put your cursor over it.) Then you can select the image(s) in a pop-up window and they'll be inserted directly into the description without the supersizing feature.
For more information on Image hosting and the features available, check out our
Image FAQs.