I'm here to discuss the nature of the work, its function, the purpose thereof, and the limitations. A tall order that presents some interesting challenges to be sure, but its worthwhile nonetheless.
To start us off, there's a necessary disclaimer, of a sort: all magic has risks. There, I said it - think about what that means for a moment.
It doesn't mean that your house is going to get lit on fire, you're going to lose your job, you're going to die, you'll be maimed, or anything of the sort. It means that you could have those things happen if you made a mistake an/or upset the wrong thing in your affairs. There's a chance that things might go wrong...no certainty that they will, however.
Such is the case within every single aspect of your life, so you might as well get comfortable with that concept now. Depending on where you live and the nature of your routine, there may be anything from a 5% chance you'll get runover on a given day to a 50% chance that you'll be shot, stabbed, mugged, poisoned, or otherwise harmed. That's not a very comforting consideration to factor in, until you realize that you've gotten by every day without this happening, if you're lucky.
I grew up in something of a warzone, and I'm not terribly shy about admitting that. Folks were shot, stabbed, beaten, raped, run over, or did worse to themselves day in & day out. Crime was a constant, and it shaped how I lived and survived as a kid. I made it out alive by using my instincts, my wits, and my magical aptitude. As a result, very little deters me now unless the risk would outweigh the value of the reward.
Demonolatry and any sort of work involving demonic magic is that way too. By going that route, you're staring into the eyes of some pretty nasty spirits that are, in some ways, criminals. You've got your gangbangers, Dons, captains, lieutenants, and so forth of the spirit world too, and some of them are demons or are demon-like in their countenance. Others are demons by birth, so to speak, and the label simply tells you what they are and where they come from (and please don't think, for a moment, that all demons come from Hell, as that's nonsense with no large basis in fact).
Some are more harmful to human beings than others. Many play favorites, or otherwise choose folks that they like more than others. This changes their interactions with those lucky ones, though its not necessarily unpleasant or pleasant - it depends on the person, the spirit, and the moods of both on that particular day.
When properly motivated, they can be hitmen, of a kind, or extremely fierce protectors who find purpose and worth in taking care of the needs of a chosen person or family. Depending on their individual skillsets, they can be healers, financial whizzes, skilled advisors, mechanical geniuses, or gifted teachers. Some are just as good at taking skills away, modifying them, or using them against a person. As with people, they are just as varied as we are.
Thus, the risk involved with working specific entities depends on them and how they feel about you. If you're a narcissistic individual, they might either like you or despise you. If you're an honest man, that can frequently generate more interest from them than being a dishonest one, as the quality of your character is as important to spirits as it is to people.
If you happen to be dealing with a particularly regal spirit who happens to respect your bloodline, as can occur, then you're in luck and chances are that you won't be risking quite as much as someone else. You may get better results than your constituents. The trick is to find a demon that you can get along with who is also willing to get along with you. If unsure, give offerings and divine to see if the spirit is willing to help you. If you're gifted enough to see or hear them, talk to them, ask questions, and see how they respond. Should you choose to ask them what they're good at, chances are they'll tell you. If you treat 'em with respect, they're more likely to do what you want.
And when in doubt, ask someone who knows the spirit in question better than you do.