Every casino and website has a group of oddsmakers at their disposal who comes up with the point spread for the NFL game, the over/under total and the money line odds. These people are highly skilled at their trade and have a vast amount of experience in the industry. The Vegas NFL line, which comes out of the Las Vegas casinos is the most used and also considered the most trustworthy in the business. The job of setting the line is not the job of one man. It is rare for an individual oddsmaker to set a line by himself.
Most sports books employ teams of oddsmakers who meet with each other and pool their knowledge before they agree on a betting line. Becoming an oddsmaker isn’t easy — there are no oddsmaker schools. Plenty of books describe handicapping and oddsmaking, but the only way to get an actual job as an oddsmaker is to have lots of experience.
Most NFL oddsmakers used to be gamblers and/or took bets illegally at one time. Some of them learned the business through their families or friends, while others just watched and learned from others before them. They watch sports constantly, read dozens of websites about sports, and have friends and contacts around the country to provide detailed information on every team and every game.