There is also nothing wrong with doing what i said.
As a librarian, I say there's plenty wrong with that. It's stealing, even if you pay your fine for "losing it".
If you suspect a book is rarely borrowed (and the library's computer system is able to tell them the frequency of its circulation), make an offer to buy it. Libraries do sell off "slow" books.
A few years ago, when first edition Harry Potters were getting huge money on eBay, libraries were reporting them going missing. A library I knew put its own first edition hardcover onto eBay - and used the money to buy lots of later MMPB editions to quell demand. It should be the library's right to profit in this way, not some sneaky patron.