You have to ascertain the company’s revision policy. They are supposed to offer free revisions. This is because they produced the work and you paid for it. If you do not like it, as them to revise it to meet your expectations.
Some of those sites employ non-native speakers and writers without university degrees and that might impact on the quality of their works. To avoid this, read as much custom reviews as possible. You can also check the requirements for applying on the service as a freelance writer.
This includes the general mistakes that you make especially if English is my second language. Your writer also needs to be aware of the books and materials you have used in your class. He can use them as referrals when handling your assignment.
Round-The-Clock customer service is no last thing because it ensures the order will be done in time and exactly the way you wish. There are always unexpected issues and questions that might appear, and the most convenient way to solve them is to use customer service, which should be available at any time. Bear in mind that not every essay writing service has direct lines with staff and implies communication by emails and there is no warranty your order will be done in time.
Every person has a writing style that most professors are able to tell because they have marked your work for long. As such, the writer that you settle for must be able to match the essay with your writing style.