You figure they could tell you BEFORE you buy the admission ticket. The least they could have done was communicate to the main gate ticket vendors that the GoT exhibit is sold out for the day so we don't feel ripped off?
It's a disgusting money grab.
It's like purchasing Beyonce concert tickets. Then you are settled in to your seats only to have the announcer tell you last second that Beyonce is sick so Rebecca Black will be performing for the night, no refunds!