I don't understand the term "smoked."

 

The usual pre-purchase checks, applicable for any vehicle. History, title, etc.

You should also find out why the lights don't match (if in fact they don't. It could just be the angle of the photo). Look at the bumper alignment closely both sides, measure any gaps between bumper and bodywork.

Check in the boot/trunk behind the trim panels for any obvious signs of repairs or creasing in the panels and stiffener bars.

(Motorm, smoked, not clear red when unlit, looks a bit like a dark greyish purple towards black on a red light, or on an orange indicator light almost black when unlit.)

(Jon and Motorm, on the indicator orange lenses this smoked look can be achieved with a filter fitted in the back of the lens, which could simply have been lost when routinely replacing a bulb, it can also be achieved by lightly spraying the inside of the lens with black paint or lens smoke paint, not recommended but I have seen it done).

 

Did you end up getting it? Keep in mind, even if the tail-lights truly do not match, there is such an abundance of excellent condition used parts available for the x300 right now on Ebay and such that you should have no problem sorting that out correctly for very little money. But I agree, it was probably an issue with lighting and photography.