Short answer: it is real work and real money, but it is not employment, and the difference matters more than most people expect.
What you actually get
You get paid per completed order, keeping a share of what the client paid. You choose what to take and when. Nobody assigns you a shift and nobody stops you taking a month off.
For a lot of players that is the whole appeal. You were going to be in the game anyway.
What you do not get
This is the part worth reading twice.
There is no salary. A quiet week pays nothing. There is no sick pay, no holiday pay and no notice period, because you are not an employee anywhere.
Income is uneven by nature. It follows demand, and demand follows the game: a big update or a launch brings a flood, a dead month brings very little.
And it does not scale past your own hours. Every order costs you time at a keyboard, so there is a hard ceiling and it is the number of hours you are willing to play.
Who it suits
It works well as a second income for someone who already plays a lot. Students, people between jobs, anyone whose evenings are already going into the game.
It works badly as a plan to replace a salary. Not because the money is bad per order, but because nothing about it is guaranteed month to month.
What separates people who last
The ones who keep getting orders are not the strongest players. They are the ones who answer messages, finish what they took, and never touch anything that puts a client's account at risk.
Boosting runs on trust. The client hands over an account or their evening, and there is not much protecting either of you except reputation. People who treat it casually leave quickly, usually after one bad order.
The GTA 6 angle
There is a specific opening right now that will not be there in a year.
GTA 6 launches on November 19, with the online mode following after. When it opens there will be a rush of players who want progress immediately, and almost nobody with real experience in an economy that does not exist yet.
The teams preparing for that are recruiting from GTA Online in GTA 5, on the reasoning that the routes will change but the habits will not. Getting in before the launch means learning the new economy alongside everyone else rather than behind them.
If that sounds like your situation, the booster jobs page lays out the terms.