On April 1, 2010, Rackets were replaced by Properties. This article describes the obsolete Racket feature.
Rackets were a replacement for Properties for some beta accounts. There were tiers that opened up after you mastered the first tier of each racket. For example, when you mastered the Three-Card Monte racket, a new tier opened up called Backroom Poker. Mastered that and Executive Game opened up and so on and so forth. You had to return to collect on the racket after it was completed or it got busted by the cops and you lost the money and the influence.
The Attack, Defense and Job rackets each generated an initial count per instance, until the job was mastered. After mastering, you were then awarded an additional boost each time you collected the racket. For example, the Taxi Stand Racket initially generated two Free Ride boosts every four hours. After you had mastered the racket you were awarded with three Free Ride boosts every four hours.
http://mafiawars.wikia.com/wiki/Rackets#Job_Rackets