It wasn't really an issue until the 1830's, as prior to that the candidates for the presidency were decided by the elected officials of that party. There really wasn't a formal process for deciding who ran, but what often happened was all the congressmen of the party got together and people threw their hats into the ring during these meetings.

It wasn't until the Anti-Masonic Party realized that they could be on the ballot in enough states to have a shot at it in 1831 did this system not work. After all, the Anti-Masonic Party didn't have any congressmen. So, they called a caucus in all the areas that they had big support, sending big wigs with all the information from town to town to get a feel for how the rank-and-file felt about the choices.

The Anti-Masonic Party didn't come close to winning the big office, however, and they merged into the nascent Republican Party that around the time of the Civil War. That meant that the two major parties didn't have a presidential primary of any sort until Florida enacted one in 1901. The process then spread slowly, and the Convention where the party elite still controlled the process was the final decider until the chaos of the 1968 Democratic National Convention where Vice President Hubert Humphrey secured the nomination despite not winning a single primary.

There simply wasn't a time when Americans were generally illiterate and they had primaries that mattered.