The CRT (Consejo Regulador Del Tequila) has two classifications of tequila: 100% Agave and mixtos, though the latter will never be labeled as mixtos and will just say “tequila.” A 100% Agave is exactly that, a tequila that is made with 100% steamed, mashed, fermented, and distilled agave. One that is not labeled “100% Agave” can be made with up to 49% non-agave alcohol. Corn,sugarcane, or other grains, just to name a few. We’re not going to point any fingers but it’s believed that these tequilas made with questionably distilled alternative non-agave alcohols are responsible for those brutal post-tequila hangovers that we all enjoyed before we were legally allowed to drink.
If all else fails and whatever you buy ends up tasting lousy, just add a little fresh squeezed lime juice, agave, and ice, make a margarita, and call it a night. Remember, there is always a next time and practice makes perfect.