Generally, all the fake level x cards I've seen don't have holo borders, sometimes don't have holo pictures either, can have spelling errors, and are printed in a different font from regular level x cards. I think the easiest way to tell is from the border and the font, if you look up a picture of the real level x on google images or something and just compare it side by side with the ebay image then it should be apparent.
The other thing to watch out for is world champion deck cards, these are released by pokemon as collector pieces but aren't playable in tournaments. There is a huge problem of people selling them as regular level x's on ebay right now, the way to tell them apart is that they are completely non-holo and have a signature on the picture.
