from most any nation it is obvious that they are designed to be incrediblely difficult to forge.  Even a mediocre forgery would be much more expensive than fakeing a state or military ID card.  And aside from a visa stamp being a poor indicator of authenticity they are often quite difficult to read, smudged.  It seems that buying a drink would be the last reason someone would forge a passport.  And if they did it would likely be an underage US citizen. If there is any doubt about the authenticity of the passport then the vendor can refuse to sell it to the person.  This is complete bullshit.