Grileiros are infamous throughout pioneer regions of Brazil for land theft and land fraud, for example in the 1970s they were active in Goias, but now are more active in Piaui, Maranhao and other frontier regions. A typical griliero will create a land title for a piece of land, often a large piece of land, which is usually un-cultivated. These un-cultivated lands, especially in areas that are not fully incorporated into the agricultural production system, are often ambiguous in terms of land ownership. Often someone years ago demarkated an area for ownership using natural landmarks such as trees, streams, and hills and these demarcations may have overlapped with others. However these conflicts did not much matter because there was little economic interest. Here enter grileiros. They find lands that have ambiguous ownership and create their own titles. They are known for using crickets to age these documents (this is where the terms grileiro and grilagem come from) to make them look authentic. They then act as real estate agents and sell these fake land titles to prospective farmers who are often coming from outside of the region, and sometimes outside of the country.
The new owner will then clear the land, begin producing, and then discover that another person or multiple people have claims on the same piece of land. This could be the original owner or another new owner who the grileiro (or another grileiro) sold to. Thus begins a long and arduous legal process to determine the true owner of the land, during which time the land is usually left to fallow. The grileiro is usually disappeared by this time.
Grileiros also are known to create titles for reserve land. Reserve land is a legal requirement in Brazil. If a farmer buys land, they then have to buy a piece of natural reserve to be left uncultivated. The amount depends on the state, and can range from 20% to 80%. Grileiros' role in this is to create multiple titles for the same piece of land so that a single piece of reserve can be used by multiple farmers. The farmers are sometimes complicit and sometimes not.
Many of the early North American farmers in Bahia who I have either spoken with or heard about through secondary sources had serious problems with grileiros. Many had land taken out from under them, with little option but to return empty handed to the United States. One was actually killed in a dispute with grileiros. The same happened to many Brazilian farmers in the region and is happening now in new frontier regions of soy. I haven't heard much about this here in Goias, perhaps because the Mennonites were here long before anyone saw any value in the farmland here.
This is what people are talking about when they say that Brazil's soy frontier region is the Wild West. To some extent the representations of Brazil as a lawless place are based on stereotypes and pre-conceived notions, but the threat of grileiros is a real threat; both in terms of economics and personal safety for farmers.