When someone steals merchandise offered for sale in a retail store it is generically called shoplifting . Shoplifting most often occurs by concealing merchandise in a purse, pocket or bag but can occur by a variety of methods.
Most shoplifters are amateurs.
However, there are growing numbers of people who make their living by stealing from retail stores. Amateur shoplifter can be highly skilled, and some steal almost every day, but don't do it to make a living. Most amateurs are opportunistic, crude in their methods, and are detected more often than others. Professional shoplifters run the gamut from being highly skilled to thug-like. Some professionals work in teams or use elaborate distraction scenarios.