Mercantilista translates to 'mercantilist', a word tied to old economic theory about trading purely for profit. It is a surprisingly sophisticated term to hear in a salsa song, which makes it stand out and gives the lyrics a sharp, almost scolding edge.
Oscar D'León uses it to call out someone obsessed with money and material gain, like a walking calculator. He sings "Mercantilista, te compadezco" ("Mercantilist, I pity you"), pitying this person for being so consumed by profit that they miss out on the simple joys of love and life.
Oscar D'León spends this whole song accusing a woman of doing arithmetic where her feelings should be. The charge is specific: her words, he says, "Son de un contador mercantil" ("Are from a commercial accountant"). Then he does the arithmetic for her, and the chorus turns into a times table: "Dos y dos son cuatro" ("Two and two are four"), "Cuatro y dos son seis" ("Four and two are six"), up to sixteen and then round again. The joke gets better the more the band repeats it, because the horns keep swinging while the lyric turns into homework.
What he offers instead is himself. "Hay que ser como yo" ("You have to be like me"), he sings, "Bohemio y poeta" ("Bohemian and poet"). The pity in "te compadezco" ("I pity you") is real, and so is the smugness. By the sonero section at the end he has stopped arguing and started reporting: she sits with the calculator working out "Cuánto al marido le va a sacar" ("How much she's going to take from her husband"), and her heart "palpita" ("pounds") over inflation. That makes it an odd bargain of a song for a Spanish learner, since the chorus drills the numbers while the verses hand you the vocabulary of money and blame.