The medieval Church lasted from before whatever year you call the beginning of the Middle Ages to (at least to some extent) after whatever you call its end. Surely along the way, there were priests, friars, and reckless heretics who purposefully misinterpreted the Bible to gain money or power.

...But if a priest wanted to exploit people for personal gain, depending on Latin literacy and illiteracy to covertly misinterpret the Bible would be approximately the least efficient way to do so. And eventually, pretty stupid.

First, we absolutely have records of bishops, theologians, and other Church officials complaining about parish priests getting the Bible wrong. But the criticism has nothing to do with purposeful misdirection. The problem, they claim, is that the priests can't read Latin.

Whether or not this claim was widely true (the extent to which is was is a matter of scholarly debate) is immaterial. The point is that higher Church officials sometimes had one or another reason to accuse lower-ranking priests of Doing It Wrong.

Second, priests' access to Bibles was limited. Paper wasn't really introduced to western Europe until the later 14th century. But even the gradual change from parchment to paper didn't change the fact that the Bible is a really long book, and prior to 1470 or so was being copied by hand. Some parishes and dioceses were rolling in money; most weren't.

Third, until sometime in the 1400s, the Bible itself was a lower priority than you might expect on the list of books a parish would want. The most important were books for saying the liturgy--all the stuff around consecrating the Eucharist, prayers for various points of the liturgical (religious/ritual) year, and so forth. Probably second were sermon collections. Even after the introduction of print, breviaries and other liturgical texts received the most editions by far.

Fourth, and related to the above, the Bible was not the central axis of religious instruction from priests to the people before some time in the 1400s. (We'll get to that part.) Moral instruction--the majority of religious teaching, and generally what we think of when we envision 'social control' through religion--was organized primarily around the seven deadly sins and their various spinoffs (the four sins that cry to heaven, &c). These groupings are not biblical. They're an outgrowth of monastic life in late antiquity.

Fifth, Cagematch: Latin vs. Vernacular, Round 1. The medieval Church (and here I am focusing on 1000+ CE, when Church officials started getting concerned with heresy) was not truly opposed to the Bible in the vernacular. There are vernacular Bibles that we know were in lay hands, and made for lay hands, by the 13th century. The Church did not like lay people--especially women--preaching in the vernacular (or, really, in Latin) in public. There are some interesting geographic differences here--we don't have any surviving vernacular Bibles from medieval Iberia--but in general, there was absolutely albeit incredibly limited lay access to Bibles in Latin and their vernacular.

Sixth, Cagematch, round 2. With Bibles still monstrously expensive and fairly rare outside monasteries, Church scribes and then lay clerks trained by the Church and then printers easily overseen by the Church created/popularized different ways to make vernacular Bibles accessible to readers in pieces. The most popular were probably plenaries--books that offered the Bible passages of each Sunday and feast day reading, that is, the source of what a preacher would read and preach from for each major day of Church attendance. We know lay readers used plenaries for this purpose by notes in margins, or the dates of various readings marked off.

Seventh, even vernacular literacy was still extremely rare among lay people by 1500. Scholar guesstimate maybe 30-50% literacy rate in the largest and most culturally-connected cities, like London or Augsburg. In rural areas, where almost all western Europeans lived? Negligible. Exploiting Latin literacy at the level of preaching? Why bother.

I could keep going, as I'm sure you can guess at this point. The attempt to use indulgences as the pinnacle of the "exploiting Latin" argument is especially silly. Indulgences, while part of Christian theology for centuries, were not the massive craze that Luther (correctly) depicts them as until...drumroll please...the printing press.

And besides, I like the idea of seven deadly sins, seven virtues to oppose them virtues, and seven points of this argument.