Tomax and Xamot v1's main area of concern is that their shared skyhook and rope are missing. Paint wear to their chest emblems are the most common place for paint wear. Besides Xamot's scar, the twins are mirror images of each other - exact reverse copies - one's right is the other's left - right down to the parts of their hair.
Tomax does not have a scar. Tomax has the silver shoulder and neck guards on his right side. Tomax has the red Cobra emblem on the left side of his chest.
Xamot has a facial scar on his left cheek. Xamot has the silver shoulder and neck guards on his left side. Xamot has the red Cobra emblem on the right side of his chest.
As any diehard G.I.Joe fan already knows, Tomax and Xamot are the same name spelled backwards.