This title can be true too often!
When ordering an article, I try to provide as much information as I can. Also, I include some previous relevant writing samples for a help.
There are many different writers, from really good ones to bad ones. The part that takes me most of the time is checking articles they send to me.
I have to check if they followed guidelines, proofread, and sometimes even fix mistakes if I realize it will be quicker to do it myself than to wait again for a second version. But I still them about the mistakes to prevent it from happening again.
I noticed one interesting thing - once they gain your trust, quality of articles will drop. So it's important to warn them about it each time.