Qualifications
Since there are so many different types of sales jobs, the qualifications to supervise the sales staff vary wildly. For retail sales, supervisory jobs require simple qualifications. At minimum, you need a high school diploma and some experience on the job.
In a small business, "some experience" might be as little as six months to a year before you move into a supervisory role. The best way to move up is to follow the rules, be able to motivate others (rather than threaten), play fair with everyone, and don't pull rank unless you absolutely have to. Basically, just be a good team player, and you'll boogie up that corporate ladder with ease.
For service industry and industrial sales, almost all supervisory jobs require a bachelor's degree in business, marketing, or a related field. You'll also need experience in the industry.
If you've set your sights on one of the higher-paying sales worker supervisor positions, it's likely you'll need a master's in business administration or other advanced degree to get the job. Many working professionals take advantage of company tuition benefits to pay for an advanced degree. Most colleges have online or weekend classes to meet the needs of working students, too.
Getting into an MBA program requires a good GMAT score and deep pockets. Many of the top business schools in the U.S., like Duke, Northwestern, and UCLA, cost about $120,000 (source) for their two-year MBA program. But, statistics (which you'll have to take) show the ROI for an MBA is A-OK. What's ROI? Return on investment. It's much simpler than WYGFYM—what you get for your money.