I believe the number of smart minority who are making money by sports betting over long haul is "definetely" less then %1.
I used to be a Professional Handicapper too. I remember the day, I had quit my day job and started to work Full Time Professional Handicapper. I had my own service, had many clients from different parts of the world. It's a tough job. Bad swings, unfortunate losing streaks are unavoidable.
After I started arbing, I lost my motivation to handicap games and terminated my handicapper service. Time to time, I take some bets too but not often. When you full focused on arbing, you lose your motivation for handicapping.
However, I don't think we should not be betting. Value betting/Dropping Odds (or another profitable angle/system) can be a "good addition" to your arsenal. Just be careful with stakes!
My advice to people who want to make a living by betting on sports. Bankroll is important. Your bankroll is your inventory, it's your lifeblood. When you run out of blood, you're out of game. You must have a large bankroll and the Three Steels. Nerves of steel, Heart of steel and BALLS of steel
You should not get upset after a bad losing run. You must have nerves of steel.
You should always bet with your head, never with your heart.
And finally, you should always be ready to take the risk!
Money management is very important. I suggest to bet %1 or %2 each bet. Think it like a snowball. As your bankroll increases, your profits will increase too. When your bankroll is 50k, you're betting 1000€ each game. When your bankroll increased to 60k, you will be betting 1200€ every game. If you can increse your bankroll by %10 ever month, your 100,000€ will turn into 314,000€ after 12 months. Bet limits shouldn't be so much problem as long as you have access to Betfair, Pinnacle and Asians. Good luck!
Couldn't of said it better myself...
The question posed by OP has many variables...
soft books & high limit shops
different sports / markets
bankroll size / management
It's definitely possible but the bookmakers operate due to those who lose longterm. If one employs good money management whilst using a decent sized bankroll as they shop around for the best price and find an EDGE on a sport/market the can profit for sure... Biggest thing is dicipline... I find myself struggling with this on a daily basis... you can win 5 straight bets but what good does that do to your bankroll if you bet x5 as much on your 6th bet and lose? It's all about dicipline as it ties into each one of the points I listed above..
Shopping for the best price, betting into soft/or high limit shops, finding an edge within a particular sport/market, using your bankroll wisely all take dicipline... if it was easy everyone would be Billy Walters... the older I grow the more I learn and it's a pleasure of mine realizing that the game we play is tilted in the bookmakers favor... I do this cause I enjoy it... every dog/mut has his day.