Before you purchase a Criollo knife ("Cuchillo Criollo" in Spanish) you will need to know what exactly a Criollo Knife is and what kind of Criollo Knives exist. I hope it helps you. 
The Criollo Knife is the generic name of the Gauchos' knives. Gauchos are horse riders that live in the pampas of South America, mainly in Argentina, Uruguay and Brazil. Gauchos are analogous to the cowboy of the American west and the Mexican vaquero.
Origin of the Criollo Knife: first patterns were brought to South America by Spaniard conquerors (circa 1536).
The Cuchillos Criollos were used as a weapon in duels, which were to mark rather than kill an adversary. Besides it, they have a reputation as a truly multipurpose tool and were also used for tasks as diverse as slaughtering and skinning cattle, working leather, cutting wood, making adobe bricks and many other uses.
Terms "facon (facón)" and "punal (puñal)" are used generically to describe Criollo Knives but it is certainly wrong, as they are types of Criollo Knives.
Generally, Criollos Knives are highlighted for the handles and sheaths artworks and the blades are mentioned in second place, that's why these knives are  commonly displayed in their sheaths. It is probably due to the blades origin variety and to the gauchos antique tradition of showing their decorated knives (high decorating, high status) to the rest of the gauchos as sign of social status or bravery.
Authentic Antique Criollo Knives are extremelly hard to find and they are valued at more than us$ 2000. Some silver and gold made pieces reach us$ 8000. Nowadays we can also find excellent handmade pieces made by the best Argentine knifemakers.

Types of criollo knives:

There are 4 variants of Criollo knives and many sub-variants whose names are taken from many circumstances as the place the knife is worn, the elements that can work, etc.

1) Puñal: is the form that survives till today. Blade shape: single edged spear point with a false edge near the tip (Nowadays, only a bevel): No guard, just a button (botón), a kind of knot. Blade origin: early types from Germany, Spain, France & England; in the present time also Argentine made blades. Main use: multipurpose in countryside/farm

2) Cuchilla: blade shape: normal, single edged flat blade spine but with impressive deep-bellied edge. No guard, no button. Blade origin: early types from Germany, Spain, France & England; in the present time also Argentine made blades. Main use: butchering.

3) Facón: early type of the gaucho's knife. Blade shape: dagger, thin and long blade, very sharp point although having a single-edged blade (only sharpened on one side); Always equipped with Double guard, "S" guard, "U" guard, or Crossguard. Blade origin: from broken/obsolete swords, sabers, bayonets and even machetes (Nowadays, blades made in Argentina). Main use: defence, combat, fighting.

4) Daga: it is also an early type of the gaucho's knife. Blade shape: dagger, thin and long blade, very sharp point although it is double edged. Guard: might be omited. If it is not omited it is indetical as Facon guards. Blade origin: from broken/obsolete swords, sabers, bayonets and even machetes (Nowadays, blades made in Argentina). Main use: defence, combat, fighting.

Sub-variants: verijero, caronero, capador, picazo, fachinera, rabón, tongorí, fariñera, flamenco, fillingo, alfajor, chaucha, asador, tararira, envenao, etc.