Start looking at company Web sites. See if they seem to know their stuff. Find out how a company ships the caviar.
E-mail the companies with questions.
If they respond in a timely, friendly manner, that's a good sign. Ask for a catalog. Make your first purchase a small one. See if the caviar is fresh, tasty and genuinely what you ordered. Try to return something, or ask questions or complain to see how the company responds.