Professional athletes are the ultimate high-net-worth customers. In 2010, average minimum wage for NFL rookies was $325,000, going up to $395,000 in a player's second year and $470,000 in their third year. Average player salary, with both stars and rookies taken into consideration, was $1.1 million in 2010–for careers that typically last less than 10 years. Expensive houses, powerful cars, jewelry and high-end collectibles are all part of the picture.

But what happens when things go wrong? "Broke," a recent episode of ESPN's "30 for 30" series, examined bankruptcy among professional athletes. According to Sports Illustrated, 78 percent of former NFL players go bankrupt after 2 years of retirement; 60 percent of former NBA players are broke within 5 years of retirement. Reasons include bad investments, excessive lifestyles, trusting family, friends or unscrupulous financial advisors, and simply failing to plan for life after retirement.

The average agent and broker may not have sports superstars as customers, but you can still learn a lot about how to advise high-net-worth clients by studying the lifestyles of the rich–or broke–and famous.