Literal translation
he would kill a flea just to sell its skin
Meaning
he's exceedingly stingy
Explanation
The hyperbole pushes stinginess to its extreme by imagining that a person would be willing to kill a flea, a tiny and worthless insect, in the sole hope of squeezing out the slightest profit by selling its skin, an obviously derisory and utterly unmarketable thing. The very absurdity of the undertaking, wildly disproportionate to whatever gain it might yield, underlines the intensity of the stinginess being described: nothing, however negligible, escapes that person's desire for profit. The proverb echoes, within the same set, the one about selling a beast's hide before it has been killed, but reverses its meaning: where that one denounced reckless anticipation of a gain, this one denounces greed clinging to the tiniest possible gain. The word niero means flea, and the verb tua (to kill) remains direct and concrete. The expression belongs to a familiar, comic register, reserved for the affectionate or blunt teasing of someone known for their tightfistedness.