I would think that it would be extremley dificult to open a new sportsbook and make money in the first few years.
1) for every dollar that is sent to you, assuming you will cover fees, you'll only get $0.96. So if soeone just rolls thier money once, on average all you have done so far is make back the money you lost on deposit fees.
2) in order for a new sportsbook to attract new customers, you are going to have to give away incentives. These incentives or bonuses, cost you money.
3) Typically a large percentage of players that will be willing to risk funds at a new sportsbook are experienced middlers, scalpers, and whores. So while maybe your thoeretical hold on sqaures is about 5%. ON these players its probably cloer to 1 or 2%. In fact, because this is a sportsbook and not a casino, if you don't have a good linesmanager, you could actually have a negative thoeretical hold against some of these players.
4) you are going to lose to these sharp and semi sharp players. The only money you will make is after your squares first roll thoiermoney once to cover depsoit fees, than roll their money enough times to cover the bonuses they recieved, and only after that do you start making all your money.
5) You have a long list of exspenses that need to be paid for. a) software, b) hardware c) payroll d) rent e) admonitstartive exspenses.
Probably the biggest mistake people make is confusing a casino with a sportsbook. At a casino you can set you thoeretical hold on any game you wnat. And you will be sure to make money on all your customers. With a sportsbook, you can't do that. If your players are sharp, you will lose. Becaus ehtye will only bet, when they have the advantage. SO the only way to survive is by being willing to lsoe money for the first few years unitl you can build up a large enough square base to support your business. Most investors in sportsbooks, don't appear to be willing to wait that long. And many also don't have the marketing know how to attract the customer base they are looking for.