Examine closely the most heavily rusted areas, sometimes the grain of the wrought iron will be visible... look for signs of welds, modern type welds are a definate warning it is not likely wrought, fire/lap-welds are a very good sign for WI.
I have a pretty good amount of wrought iron, and have never paid for any of it...but I've been lucky, and willing to drag a 50# piece of rusty iron a mile through the woods if it looked like it might be wrought. Those smaller wheels with the concave shape, I think (I could be wrong) are likely more modern thus not likely to be wrought. The larger wheels with the convex surface look very promising.