I've had those posters up for months in my trade rooms and in the past in my trade threads. I never ever once got anyone who even showed any interested in them. My thought is they are worthless, or rather worth however many credits you can get for selling them.
Even though they are a retired in park quest there has never been much interest in them. They do not trade well at all. If you were trying to sell I would think you get maybe 1,000 credits each for them.
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