I take it that you have opened a case under eBay's money back guarantee, and that the seller has sent you a prepaid return label as eBay requires them to?

If so, labels are normally bought and sent through eBay and I've never heard of any being illegible. Maybe the seller has sent one in some other way. In any event, I would contact eBay customer supporrt and let them sort this out with the seller.

p.s. just an afterthought, but are you sure this isn't something to do with how you're trying to print it? Normally you can scale the image size up or down as you want. You're not perhaps trying to print a thumbneil image?