I used to be a manager for a very large loan company, and it was absolutely imperative that the good payers were NEVER allowed to leave. Once they got to a point where they owed, say, 30% or less of the original total amount oustanding (loan plus interest) we would bombard them with offers, dream kitchen, new car, luxury holiday etc. Phone calls to flatter them into believing that they are very special, best customer etc, were also commonplace. The best part of such a sale was that you encouraged the borrower to use some of the new loan to pay off the old one before it had finished, thereby smashing your issue (selling) and collection targets at the same time. The fact that this meant paying interest twice on a proportion of the original debt was never thought about or discussed.
I don't apologise for it, for what it was it was a fabulous job, I had a young family to feed and it paid my wages, I also would say that I knew no different. A Barclaycard, for example, with £3k on it can take up to 48.5 years to pay back at minimum and will cost nearer £12k. As a business model it is absolute genius, as very quickly people end up borrowing their own money back and paying interest to someone else on their own money!!!