[fjtorres]

Doing a proper serial isn't about taking any old novel and breaking it apart to charge more.
(The Kindle serials sell as bundles for about the same price as most indie ebooks. See the link above.)

It is a narrative form of its own, much as the old movie serials were an art form all their own rather than chopped up movies. Or, for a more modern example, look to the shorter anime series; the 10-12 episode series.

A proper serial is more like a tightly connected set of short stories, with each episode having a clear narrative arc plus links and developments that fit into the broader arc of the series. Cliffhangers might be involved but aren't required. There's other kinds of hooks that work to tie the bigger narrative together.

This doesn't work with just any old story but it does naturally fit a few, like the "grand journey" or chase stories where the bulk of the story takes place while the hero(es) go from point A to point J, encountering a series of adventures along the way. Stories about serial killers might fit the format or stories about onion-like conspiracies. Space explorers boldly going or space refugees on the run...

It's not just a marketing trick.
But it *is* hard to pull off.