Pretending to be a drinker versus accepting a protection gig...for a cop? Not only is this a no-brainer, but MANY people in law enforcement take on extra duties and second jobs as personal security. Completely plausible and realistic. (Consider how many undercover cops get involved in drugs, alcohol, and sex issues.)
But more importantly, we have a young, green officer on his first undercover job. And he needs the money. He is also interested in the girls. Very likely for him to kindly accept money, or entertain the idea, so as not to make her question his motives any further.
No doubt our young friend will come under scrutiny in the future as his role deepens and the plot thickens. Are all of these girls innocent? Seems unlikely. Someone somehow is involved in the investigation. He will be investigating them while he, no doubt, develops feelings for them. Being the "hired help" providing security (or keeping an eye on) Afina provides cover for spending more time with her, as well.