I know just what you mean. I figure if it's so hard to tell, then it doesn't really matter. Nevertheless, I try to figure it out by looking at the weave. The right side appears "smoother" for lack of a better world, while the wrong side is slightly "bumpy." Those are just the words I made up in my small brain, but someone else might describe it differently. Try looking at a solid where there is an obvious right and wrong and it will help you see what I'm talking about. It's easier to see on a solid, but a print will work too. You just need to look at something with an obvious right and wrong. I work with batiks a lot and I'm sure I've mixed some right sides and wrong sides, but I've never been able to tell.