Belford University is a diploma mill. Ashford is an accredited university. A good way to tell a university or college from a diploma mill is the financial aid policy. A diploma mill will not accept federal financial aid (they can't!).
Independence University is accredited by the Accrediting Commission of Career Schools and Colleges (ACCSC), so no, it is not a diploma mill. A diploma mill is an unaccredited institution which gives out diplomas for a fee and does not actually offer an education.
Liberty International University is NOT a diploma mill. It's a accredited University, its just not a good one. The school is in a bad part of Tampa, its in a old run down office park on top of a UPS store.