It is very possible to make money by betting on tennis matches. However, like any sport, it is very rare for someone to consistently make money in the long run when betting. Sportsbooks are the institutions in charge of taking bets and paying out winnings, and they almost always win. In fact, the last time sportsbooks in Nevada lost money over the course of a month was in July 2013. Their dominance happens for a few reasons, but primarily because the sportsbooks have access to and apply all publicly available knowledge when setting their lines, and do not have a vested interest in any of the matches.
Bettors who are experts in the sport are highly disciplined with their money and bets, and those who understand and apply statistics have a much better chance of making money betting on tennis or any sport for that matter. Those who aren't experts will sometimes have short-lived lucky streaks in which they win large sums of money, but then they tend to get too confident and throw all that money away on other bets because they feel like they can make more.
Generally speaking, it is not smart to bet on tennis or any sport at all unless you are an expert in the sport and betting in general. You also need to have extremely high levels of self control and a nonaddictive personality. Even then, the chances of making money in the long run are not as high as most people tend to think.