Creating any kind of freelance artwork for any kind of client comes with the largest risk of all, not getting paid and being expected to work for exposure or work via bartering. Not in all cases is this a bad thing, in the case of bartering you are at least getting something physically tangible in return and you can be fairly certain of what that item is.
In the case of being paid for exposure, this is far more subjective and is difficult to measure as a form of payment. Getting exposure for work requires transparency and an understanding of what the creative is getting and what the client is giving. How would getting a promotion boost actually affect me, and the more critical question, would the client even actually give me all that much of a benefit in the future?
Creative work is valuable, far more valuable than many creatives believe, and as a creative you should assign value to your work, preferably monetary, but make sure that you are actually getting something for your work. Know what you want, and document it in the form of a contract. Get paid for your efforts.
Resources: Brad Chow- Should you work for exposure https://www.youtube.com/watch?v=CLBWAodEy6k