Meaning of "to charm the skin off a snake"

Solution 1:

The phrase simply means to be extremely charming.

It's a variation on other such phrases, the most common of which is probably to charm the pants off someone. Googling around gives you plenty of other variations - charm the knickers off a nun, charm the pictures off the wall, etc.

The idea is that the character is winning enough to be able to separate two intimately bound, seemingly inseparable things.

Solution 2:

There may be two ways to look at it, depending on the context.

It might be intended to mean that the bartender is charming enough to get someone to part with something that is very close to them. However, it is a bad analogy. Snakes shed their skin periodically so getting a snake to part with its skin is very easy and would not necessarily require any charm. If this is a deliberately bad analogy then the author intends to mean that the bartender isn't especially charming at all.

Without knowing more about the context it's hard to judge whether the expression is intended with or without irony.

EDIT: Looking at the reference, provided by OP, here is the next sentence following the expression in question:

The ability to do just that came as naturally to Rick Wells as breathing. It was an ability, a gift, really, that Rick depended on but didn’t pride himself in. There were many ways to hide from life, he knew. On a bar stool was one way. Behind a killer smile was another.

Based on this, it is pretty clear to me that the author intended the expression without irony. Therefore I would go with the interpretation that the intended meaning is "very, very charming" but for the reasons I pointed out above, the result is rather more confusing than effective.

Solution 3:

The expression is in reference to the fakir's display (a performance) whereby a venemous snake, usually a cobra, is said to be charmed by the sounds played on a reeded or recorder-like wind instrument. The imagery is of the snake's rising up out of a basket, next to which the entertainer is seated, swaying and playing his instrument, and displaying a splayed hood, which is normally both a defensive threat and prelude to strike, but refraining from further aggression--the subterfuge being that the snake has been charmed by the player's lilting musical sounds--the reality being that the player's swaying movements (before an animal without stereoscopic vision) stimulates the hood threat but incapacitates the snake's capability of "acquiring" a strike target. The simile, to lure a "snake out of his skin" broadens and exaggerates the snake charmer imagery to encompass person to person interactions. As to whether or not the simile extends so far as to include people-so-charmed's also being of snakelike (reviled) nature, the passage seems to say it does not; but its being in the Keys (where cobras are not found), and attended by copious drinking, also suggests that it might.