I have noticed several ways of getting free miles for a little work. Certain merchants will let you return merchandise and give you cash back instead of a credit card refund (they prefer it, actually, since it is quicker to do). This is also a cool free cash advance. You can also do this in some universities: enroll for a course, pay for it, then drop out during the 100% refund period. Many schools will send you a check.

My question is: why is this not a popular method? Is this unethical in some people's minds?