Sad to say, some freelancing opportunities, won't be opportunities at all. They'll be scams designed to steal your time, money, or reputation. I can't give a canonical list of scams floating around out there because the criminal nature is to develop new techniques as people get wise to the old ones. But here are some warning signs the prospective job just isn't worth taking. The first kind of scam is one that makes the rounds a lot.
You get offered a job but with a non-specific amount of pay. For example, let's say they offer you a share of profits. Well, how will you know how much their profits are? Are their books publically audited? Probably not, which means they could offer you any amount or nothing at all, and you'd have no real recourse.
Tied to that one, is the offer to pay you in something other than money, most often in the company's products. Now that's great if you really want their products and they're being offered to you at a higher rate than cash would otherwise buy. But here again, the control is mostly in their hands. What if they stop offering the product you want, what if they go out of business, do the products even exist yet, what's mechanism for delivering them to you?
A variation on this is the promise that you'll get exposure or a great portfolio piece in exchange for your work. This isn't a scam per se. It's just that in my experience, jobs that pay well make much better portfolio pieces. Having said that, you might actually decide to take such work when you're first building your portfolio. Just be sure to appropriately value what they're offering. Now personally, I can't remember ever finding the value of such exposure to be high enough for the work required.
The third warning sign arises if your client asks you to do something illegal or immoral. As an architectural illustrator, a client will sometimes try to accompany my work with videos or graphics that they snagged online, and that they don't have the rights to. They've already shown they're dishonest or immoral. What makes you think they'll be honest and moral with you?
Another warning sign crops up when you get an offer out of the blue, but you can't really determine the name, location, or contact information for the source. The issue here is one of enforcement. If they mistreat you, you'll have no way to go after them.
Finally, we get to the classic work-at- home scam, where you're required to put in some amount of money to make the deal happen. Let's get something straight. You're going to have business expenses as a freelancer. But none of that money, and I mean zero dollars and zero pennies should go towards someone who is allegedly offering you work or to any other source that you don't choose. This can be tricky. Maybe the client requires that you get some sort of special kind of equipment, or certification but that it's only available from one source. Check it out. There's a chance that, the source is connected to your so-called employer and that you'll never see a penny of work in return.
It is possible that you'll take a job that has one or more of these warning signs, and it will turn out just fine. For example, start-ups sometimes offer equity or stock instead of payment. That stock sometimes ends up being valuable. But this list is based on the likelihood that something is a scam.
These warnings aren't absolutes. When you're deciding which jobs to take, you'll be playing the percentages. Just realize that jobs that have these warning signs carry a higher risk than those that don't.