"Is this really true? If it is, why do people bother?"
Casinos and bookies advertise themselves as cash machines/ATMs. They give the illusion that all you have to do is walk in, place a bet, and walk out rich. People want money, and they don't want to work hard for it (myself included), that is why people try.
Counting cards is from a bygone era. A modern shoe with 8 decks will only deal half the cards (if that) and then be replaced. (Cue the flood of pro-gamblers who regularly count cards and break the bank at Monte Carlo every weekend before flying back in they personal yacht to moor up at the Vegas docks).
I used to arb a lot about 6 years ago, and never had a single problem with bookies trying to limit my account. Why? Because I am losing as many bets as I am winning. Even when I was using a bookie for the win and tie, and a 2nd bookie for the lose, there where never any problems. I was just a single user amongst thousands of others who where either betting based on their star sign, tarrot reading, betting that the horse will lose because it won last time, betting that the horse will win because it won last time, betting that the team will lose because they are playing away, the combinations are endless.
The number one sales pitch for any gambling system or tipster is "Don't be greedy!!! If the bookie learns how much money you are making, they will try to close you down!!!"
No, they won't. They couldn't care less. You are a tiny tiny tiny cog in a massive machine. They don't care if you win 1 bet, then lose the next (because your arb won at a different bookie). Casinos even sell books in their casino gift shops about how to win at blackjack/roulette etc. Casinos and bookies love the system sellers. Every time someone buys a "Brand new system that will kill the casinos!!!!!!!" the casino will make money, because counting black and red and doubling your stake each time is going to wipe you out long before you break their bank.
I get huge amounts of spam and physical junk mail for gambling systems and horse tipsters/systems. I find it amazing that so many horse systems exist and apparently seem to make money. They are generally either betting on the horse that won the most, or the 2nd favourite, or betting against the horse that won the most. Yet these contradictory strategies all seem to have achieved "2000% return on investment this year alone!!!!!!!" etc etc Some sort of Schroedinger's Horse that has both won and lost simultaneously? One would almost think they were being a little flexible with the truth.
Arbitrage trading (to make it sound grand) is a good deal if you can spend the time. But it does get your heart racing when one of your bets doesn't go through because the odds have changed and you have to scramble to Betfair to try and limit your loss as much as possible.
Zero-risk? I think not. Low-risk, yes. You are never going to get wiped out, there will always be an exit strategy to limit your losses (e.g. bet £100 in total across 2 bookies, and you might only get £98 back instead of the £102 you were looking for because the odds changed and that was the best deal you could find.) Still better than losing the full £100 by betting on Manchester United because they are playing at home and Jupiter is rising, or any other system that someone tries to sell you.
The biggest issue I have with Arbs is the same as with any other gambling system. IF IT MAKES SO MUCH MONEY, WHY SELL IT? Seriously, if the guys selling the Arb info believe it is so good, why bother with the whole websites, and selling, and credit card companies to handle payments, and fraud prevention and stolen credit card numbers etc. Why not just make a billion keeping the info to themselves? The answer is, because it is time consuming and fiddly. Bear that in mind, they find it easier to do all of that, then sit down in front of their PC and get "Free money from the bookie."
Not to be confused with gambling systems, which are all nonsense. "Find out how to use the casino as your own personal ATM and get millions in free casino money!!! Only 20 copies available for only £97 !!!!!!!!!" Yeah, right. Believe that at your peril.
I gave up arbing because the big bookies stopped having so many good arbs, and I was having to spread my money to more and more obscure bookies with annoying rules for deposit and withdraw.