I have the prs-300. I bought a disc off ebay, probably not a smart move

I loaded the books into the library and transfered them onto the reader, and thats when the trouble started. They are in comic format, something I wasn't expecting, but they're way to small to read, pressing the text increase size isn't making them any bigger, so I've put it down to a bad experience, but

is this a problem with all discs off ebay? Is it worth buying discs of books from there?

pea