I would like to interview the writer before they start work on the essay for my piece of mind. I would also like to pay in three instalments for every 500 words. I would need access to their mobile phone number and email address. Also, unlimited amendments per 500 words, OSCOLA referencing and a bibliography is essential.
If a writer is as qualified and capable as the one you're describing, I sincerely doubt that she or he is going to have time, at the peak of the essay season, to do a personal interview with you and provide unlimited amendments. Well, there's always time, of course, when the price is right. Sounds like you've got an expensive project on your hands.