How can I tell if a school is a diploma mill?

• They often have names similar to well-known colleges or universities, but fail to mention an accrediting agency or name a fake accrediting agency.
• The organization frequently changes addresses, sometimes moving from state to state.
• Written materials typically include numerous spelling and grammatical errors, sometimes on the diploma itself.
• Overemphasis on the speed and brevity with which someone can receive a degree (e.g. "Call now and have your degree shipped to you overnight!").
• Degrees can be earned in far less time than normal (e.g. 27 days) or the diploma is printed with a specific backdate.
• There is no selectivity in admissions, or any questions about previous test scores or detailed academic history.
• No interaction with professors or faculty (e.g. only two emails are received from a professor).
• Degree requirements are vague or unspecified, lacking class descriptions and without any mention of how many credit hours are required to complete a program.
• Tuition and fees are typically on a per-degree basis.
• Grade point average (GPA) and academic honors (e.g. Summa Cum Laude) can be specified at the time of purchase.