Marcos can normally be found wandering around the town of Chuparosa, and during the day manning the general store in the market where the player can purchase and sell goods. After being robbed, he will appeal to Marston to help catch the thief. He also provides the horsebreaking job in town.
Marcos and the Escalera general store shopkeeper Angel Palomares are the only shopkeepers in the game who can be encountered riding a horse or wagon outside their place of work.
Marcos, along with Jeb Murphy and Herbert Moon, and Angel Palomares, can absorb a tremendous amount of gunfire. If the player attacks any of them, they will run. But, if the player attacks them, then pulls a weapon, they will then fire upon the player, which cause the law to open fire upon them. This scenario can get very interesting, so sit back and enjoy, mostly from cover.