How do you know its not what its described as in the listing?
For example if someone sold me a Columbus Max frame and turns out it clearly wasn't, I would expect the seller to accept the return and offer a full refund.
Another example, if a seller repainted an original painted frame and attached incorrect reynolds decals then I would also expect the above too.
Personally if the steel was of a decent quality and it wasn't intentionally mis-sold, not sure if in this case it was? I wouldn't mind, because how could anyone tell without being there when the frame was made what the exact tubing is? I would at least expect the seller to say something like
"I believe it is but I cannot be 100% sure"