The three other criminals met with Munez earlier outside of Tonka Flats, and saw him with his hat off. However, they accept Artie's disguise even though Artie has a much fuller head of hair.
During the bidding, Balya produces a derringer. However, he and the others would have been thoroughly searched while they were drugged precisely so that he couldn't produce a gun and disrupt the bidding.
At the end, Artie mentions all those who died, including Felton. Felton was never identified by name or even seen on-screen except when he attacked Jim and rode away. For that matter, it's never clearly shown that he was in the cavern. Artie also says that Marchmount is dead, but the British blackmailer was alive and well in the cavern, and there's no reason he would have stayed when the fight broke out.
Gadgets: sleeve derringer on extender, self-inflating balloon in a suitcase, derringer dart and line, lockpick hidden in a broom
Disguises: Southern gentleman Emerson P. Gentry, elderly janitor
The Denver Mint only produces coins, not bills.
The guys eat hot dogs at the circus, and refer to them by that name. The term "hot dog" didn't come into use until the 1890s. In the era of the show they would have referred to them as franks or frankfurters.
Near the end of the episode when West is following Farnsworth, some guy comes up behind West and Jim tells him "Artie, you cover the back door." It is clearly not Ross Martin.
Gadgets: rifle with a grappling hook attachment, explosive ball in boot heel compartment, acid vial in sleeve extender, thermite-impregnated cord
Disguises: Swedish waiter, desert rat "Old Timer"
The supposedly heavy bar counter that the thugs knock Jim through falls apart too easily and is clearly a light prop.
Jim has scalding coffee thrown in his face but it has no visible or painful effects and there are no burns apparent any time later.
The matte shot of the Moon has a thick black line around it.
The supposedly stacked up cells in the cell are clearly a single piece: several of them are visibly fastened to the skull above with no support underneath to hold them in place.
They place the Sun Goddess' mask on the mantlepiece as a treasured token, but it's never seen in any subsequent episode.
Gadgets: spike-shooting gun and hand-winch, hidden explosive in boot heel with a contact trigger, pen-telescope
Disguise: reverend, jewelry salesman Henrick William Van de Velde
In the scene where James West springs into the hidden attic of the building where Lucius Brand was caught with the gun, wires are clearly visible when watching in slow motion.
When the stagecoach driver helps Abigail off the stage, his lips don't move as someone (badly) overdubs the actor's dialogue.
When the murderess tells her men to search Jim and "Artie," it's clear that it's Ross Martin's stunt double, who looks almost nothing like him.