I would asusme that the person who took the pics / the person who you are buying the pics from has the responsibility to provide you with the paperwork saying what he is selling you is legal. If you can not get that from them you should not be buying anything from them (spring break or no spring break).
I have never bought content - I shoot all my own stuff. SO I do not know how the deal works for the providers to prove what they have is all 18+. But from reading stuff here what I posted above is the rule you should follow.
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