I have been a professional academic writer for several years and have run into my fair share of clients who have been scammed by large websites and craigslist postings. Unless I am handling a request within my niche, it's damn near impossible to conduct the preliminary research and gain the understanding needed to write a typical junior or senior-level essay. Anyone arguing otherwise is highly suspect. Further, if you are interested in working with a writer off craigslist, do not pay 50% upfront. It's a strong indicator that the poster is either a rookie or looking to scam students. Another issue that is important to consider, and may be one of the reasons students are caught cheating even though their essays are original, is making sure the writer uses the same academic databases that your institution provides. If I have access to project muse or jstor and you don't, it's a red flag. In addition, it is important that you discuss your course and share lecture notes so your writer is able to appropriately frame the essay within the scope of your class. There are dozen different ways to write about any one topic, and if I unknowingly introduce an angle that hasn't been discussed, especially if it's advanced, then there's another red flag.
I strongly recommend the payment/exchange process that I use.
1). New clients pay 15% of the total upfront
2) Once a client requests random samples for review and they prove to be satisfactory, only then do I send the invoice for the remaining balance.
3) Once payment is received, the essays in your mailbox. You should demand these guidelines! It's also nice if the writer provides his or her cell number and sends you progress updates or is available to answer or ask questions.
Best of luck to all of you who are trying to survive college!