Well,
In a "perfect world" scenario, two MST3K fans would have walked in right after you and bought the remaining sets. However, more likely the case was that another scalper would have gotten a hold of them.
In order to make this whole thing ethical, I would advise placing them on eBay with a Buy-It-Now of the purchase price.
You have to ask yourself whether you bought the other two sets to make bank off of unlucky fans who couldn't find the sets or to keep them out of the hands of...ahem...other scalpers.
