What is a bookie?
A bookie is a person who takes bets. He sets a price, takes your money or your word on it, pays you if you win and collects if you lose. The word is slang for bookmaker, and it usually means a local, independent one.
The job
He deals a line, though most local bookies don't make their own numbers; they use the market's and shade them where they need to. He takes the bets, and decides how much he will take from each player. He settles, normally once a week, with winners paid and losers paying. And he carries the risk, so if his players have a good week, the money comes out of his pocket. I'd say that last part is the one people forget.
The name comes from the book the bets were written in. Making a book means taking bets on every side of an event.
Bookie and sportsbook
They do the same job. A sportsbook is the company version, with a counter, a site or an app, and you deposit before you bet, which is called post-up.
A bookie mostly works on credit. He gives you a figure you can bet up to, nothing changes hands during the week, and you square up at the end of it. There is no deposit and no bonus. The arrangement runs on trust in both directions, and I always thought better of the players who remembered that it ran both ways.
He gets paid the same way any book does: the price. You lay $110 to win $100, and the extra $10 on the losing bets is his income. See how bookies make money.
The bookie today
The phone has mostly been replaced by a website. A bookie rents the site, the lines and the clerks from a pay-per-head shop and pays a fee for each player. If your bookie gave you a login and a password, that is what you are looking at.
The law
Whether a bookie may operate depends on where you live. In most places taking bets requires a license, and an unlicensed bookie is outside the law. For a player that has a practical meaning: there is no regulator to go to if he doesn't pay.
So I'd judge a bookie on one thing first. Does he pay, in full and on time? Agree the settling day and the terms before the first bet, and treat the credit line as a limit he set, not as a budget; fix your own figure below it.
If the question is how to be one, see how to become a bookie.
A bookie sells a price and his word. Check both.
Related questions
How do bookies make money?
A bookie makes money by charging for every bet. The charge is built into the price: you lay $110 to win $100, and across thousands of bets that extra $10 is his living. He does not need to pick winners. He needs volume.
What is pay per head?
Pay per head is a service for bookies. An offshore office gives the bookie a betting site, the lines and the phone clerks to run his players, and charges him a fee for each player who bets that week. The bookie keeps the players, the risk and the money.
What is a sportsbook?
A sportsbook is a business that takes bets on sports. It posts the prices, takes the wagers, pays the winners and keeps a cut that is built into the odds. It can be a counter in a casino, a website or an app.