Look for or ask for third party scientific data and take it to an unbiased professional to verify that it is valid and complete. In addition to those questions, Check the companies track record with consumer groups. Older companies will have some record but new ones usually do not. . Make sure you know what you are buying. Read everything carefully.
Companies have a vested interest in presenting only the best about their product.
Be a skeptic. Ask questions and don't be side-tracked from a complete answer. At recruitment meetings, do not be overwhelmed by promises and personal testimonials of fortunes to be made. Few recruits will succeed in making a fortune, especially if selling part-time. There are laws to protect consumers from salespersons using unprofessional or unethical sales tactics such as harassment, fear or guilt to force a sale.