I apologize for the inconvenience this may be causing, but rest assure we care and we are capable of doing the job. I've spent the entire day myself researching this issue and making sure the URLs being returned from eBay don't have some additional fields we can send in the API request to get other images sizes/formats back in the response from eBay, as of yet I have not found a valid API parameter. This is an eBay issue with the GetSellerItems and GetItems API call, where in both cases eBay is returning image urls that are of lower quality, than what were originally uploaded. I can't speak for other services, but if they are retrieving seller images via a different method than the API, then they are breaking eBay's API use policy. I've also opened a case with eBay support to see of they can shed some light on why images are being returned in their API calls that are lower quality. I suspect it might have something to do with security, and keeping unscrupulous people from using the GetItem API call to copy listings in an automated fashion, but i'll see what eBay has to say.
I was hoping to have some more details about the issue before replying, but please know we are working hard to resolve this issue and all the issues that arise, as well as providing new and updated functionality based on changes eBay makes and what the market and our sellers request.