Worked for them for 2 months, first seriously and then as an additional source of income and entertainment.
The 'business model' as they call it here makes it very hard to get orders from normal customers, usually they want previews for free and never assign anyone to the order. Most orders hang around for a long time with customers not replying. Most customers I got were cunning, cheating and manipulative, and were obviously looking for a mule to extract more and more work from.

The essayshark.com management demanded writing an exclusive preview for each order I bidden on; they disallowed me to use paragraphs from an extensive archive of my previous writings. They said it somehow would be "cheating on other writers".

With orders approval being so unstable and having to write exclusive previews - you simply end up spending time 24/7 tethered to the site, working, but not earning much.

Fined me for cancelling the order on a very arrogant customer (although for clarity and fullness - I was late with it for a few hours, when the customer decided to demand "A-quality" from me, also adjusting his requirements). I did what a professional should do - if I can't deliver what is requested given the timeframe, I cancel.

Got their "Newcomer of the month" award easily.

Payments ok.
What I like about this particular company, is that they give you true money figures; not trying to cover up the fact that they take away 3/4 of your hard-earned money. The marketplace idea is nice, but operation fees are way to high, given the fact that the website offloads the duties of communicating with the customers on you.

Worked with them for a few months. Although they declare $4-15 per page, the average almost certainly stays $4. Thus, my monthly earnings dropped right around to the low watermark of starvation. Were giving me promises of access to "higher level orders" if I kept working hard, but were reluctant to do so and generally - failed to recognize my potential (from previous 3 years of professional academic writing). Very ignorant of serious issues, the writer is always wrong.

Make an appeal of a big company, have grammar and essay quality checks done by "professionals". There is a regional manager who is kind of friendly towards you, but his peers and higher-rank managers are simply despotic and fine or suspend you in case of any stand up for oneself. The friendly manager I had was simply desperate to look "professional", and several times told a certain phrase on the phone to me: "you made us look like complete idiots"; he sounded very upset when saying it, so my guess is that he was pretty much hung up on it. In all cases, these were minor screw ups, e.g. the editor has severely broken my .doc files formatting, especially the ones with a table of contents, fancy heading styles and lots of math formulas. What I meant is they all seem to have perverse ideas of what "professional" actually is.

Are ok with payments, and do the last payment despite the fact you are certainly not going to work for them anymore. Although, there might be some slight delays.