An uneven but genial comedy that riffs on America’s love of conspiracy theories, Lynn Shelton’s “Sword of Trust” doesn’t allow the improvisational underpinnings of her creative method get out of hand. The picture isn’t tightly structured and leaves room for the performers to exercise their inventive genes, but it’s not a meandering mess; while it shambles a bit, it doesn’t become one..

The person around whom the story revolves is Mel (Marc Maron), a transplant from New Mexico who runs a Birmingham, Alabama, pawn shop but gets little help from his internet-obsessed clerk Nathaniel (Jon Bass). He’s a cynical sort of guy who still feels burnt by an old girlfriend (Shelton), a druggie and self-professed poet whom he finally says no to when she comes into the store to ask for money.

He’s also visited by a couple, Cynthia (Jillian Bell) and Mary (Michaela Watkins), who ask about what they can get for a Civil War-era Union sword, complete with scabbard, which Cynthia has just inherited from her deceased grandfather. (She’d expected to get his house, but it already belonged to the bank.)

The sword, it seems, came with a couple of other items. One was a lengthy letter from her rather addled granddad, which claims that it was the sword of a Union general (either Sherman or Sheridan) who surrendered it to General Lee. That was accompanied by a painting of the supposed surrender and a certificate of authenticity. Together they all provide documentation of the “fact” that the South won the war and history has lied about the Confederate victory ever since.

Mel, of course, considers the story nuts and proposes to pay the women a few hundred dollars, an offer they dismiss. But when Nathaniel immediately takes to his computer and finds a bunch of believers—the so-called Invictucians (presumably derived, in somewhat scrambled form, from the Latin for “The Undefeated”), who are willing to pay big bucks for “proof” of the South’s victory, he reconsiders. Dickering eventually results in him and the two women agreeing to split any profit fifty-fifty.

From there the deal turns into a road trip in the back of a box truck by Mel, Nathaniel, Cynthia and Mary to negotiate with a rich potential buyer (Dan Bakkedahl), a journey arranged by the collector’s crusty surrogate Hog Jowls (Toby Huss). Along the way, they have the chance to open up to one another in monologues the actors clearly worked out with Shelton as back stories for their characters. Intervening at a couple of points are a couple of doofus backwoods types, Zeke (Tim Paul) and Jake (Whitmer Thomas), who want the sword for themselves.

The final act of the movie—the negotiation session and its aftermath—involves lots of dialogue, some surprise twists, and an outcome that mixes in some sentiment but leaves room for a bittersweet aftertaste.

“Sword of Trust” hardly goes easy on the conspiracy-minded Invicturians, but it treats them in a laid-back manner that’s less knife-edged than mildly condescending. And its attitude toward the non-believers, quite frankly, is no less mocking, though they’re necessarily allowed a degree of depth lacking in those they’re attempting to scam. The cast is fine across the board, with pragmatic Maron and jittery Bell the standouts, and the though obviously a low-budget affair, the picture looks okay (the production design was by John Lavin and the camerawork by Jason Oldak). Though there are a few longueurs and clumsy moments, Shelton and editor Tyler L. Cook generally keep things moving along.

“Sword of Trust” isn’t the cutting satire one might have expected from such a premise, but it’s an amiable ramble with some amusing, and occasionally touching, oddballs.