What you're seeing is the 'moire' effect that occurs when the pattern of the photo is slightly out of synch with the regularity of the pixels in the picture on the monitor screen.
One way to avoid it is to re-sample the picture, using different 'dots per inch', using your favourite graphics programme, e.g. PhotoShop or PhotoPaint, and do it a few times, saving each one with a slightly different title. Then try and upload them one at a time to see which one looks best on the gallery in eBay. Good luck.