The second adventure in Ghosts of Saltmarsh is Danger at Dunwater. This features the unusual case of a dungeon full of monsters that the PCs are not supposed to fight. This is supposed to be something to discover, not an expectation, but that's not always how it's going to go. Whether intentionally or not, players may have metagame knowledge (whether from reading the module, reading reviews, or perhaps even playing the original 30 years ago) that the lizardfolk are not villians and this can lead the adventure to becoming little more than a boring set of Charisma checks on the path to an easy victory.

So, what if the lizardfolk really are a threat? Perhaps instead of planning to attack the sahaugin the lizardfolk really are planning to attack Saltmarsh (maybe to appease the sahuagin)? Perhaps the alliance is being put together to oppose the sahuagin but the smugglers want them to attack Saltmarsh first (the smugglers could be aligned with the Scarlet Brotherhood). Taking this route also explains why the lizardfolk went through channels other than Saltmarsh to get weapons. I mean, really, how did these isolated lizardfolk that see no value in humans meet random smugglers in the area, and where are these smugglers from anyway?

This can certainly run the risk of being almost as boring with attack rolls and saving throws replacing the Charisma checks, but it can certainly be a surprising turn for players expecting a warm-and-fuzzy meets cold-and-scaly sleepover in the Hool Marshes.

I'd like to hear what other adjustments I should make if I go with this approach. Obviously The Final Enemy would have to be adjusted, but perhaps that's as simple as putting some sea elves into place to join Saltmarsh against the lizardfolk and their allies (like the koalinth).