
The rules of this forum prohibit any of us from recommending any company. However, now that the mods allow us to post a link to our own sites in our signatures here (thank you, BTW), your best bet is probably to just try to familiarize yourself with the previous forum contributions of anybody you think sounds potentially legitimate, and you can use the search function for that. Pretty much assume that everybody here is either a customer or someone with some professional interest in this industry.
Consider things like whether posters are straightforward in describing themselves as company reps, writers, students, or so-called "observers"; or instead of purposely leaving that section blank. Consider what other legitimate-sounding members have to say about one another and about others; maybe consider whether or not the posts of people claiming to be writers and editors
sound like they were really written by someone who thinks logically and writes professionally (and in grammatically correct, coherent and complete actual English sentences).
In my opinion, anybody who does nothing more than that would probably be able to identify several potential writers or writing companies you can trust with your first assignment...and at least twice that number of very obvious non-candidates.
If you
really want to be smart about it, start off with a small paper with plenty of time before the deadline instead of waiting until you have a big important project due in a few days to try out your first writer or company. Good luck.