You prolly don't need to know this, but
"Emptor" is buyer ("vendor" is seller) - as in emporium; place where you buy things
"Caveat" - present tense indicative 3rd person singular - sort of "He, she or it takes care"
Can't remember the verb from which caveat comes, but the imperative "Cave" (Look Out!) is used - sometimes even in english
"Cave Canem" - beware of the pooch
fwiw the translation "let the buyer beware" is very loose and a little wrong, as that would (obviously) be the subjunctive.
Sorry about this, its not often useful speaking dodo
andrew