How to Buy a Planet: The Cleremont Conjectures, Book 1 by D.A. Holdsworth
People wake up to find that the earth was sold for a few quadrillions of an alien currency. At the time it maps to quadrillions of British pounds. Debts and other things are forgiven. Alas, people later discover that the aliens plan on turning earth into a tropical resort. The aliens also like lots of daylight, so they are melting the ice caps and accelerating global warming. Earthlings consider buying the planet back. However, the payment the received is in a fiat currency that is now valued at closer to a pound. (The currency had not been used for trading, and was most closely tied to the value of ice in the earth's ice cap - which is now melted away.) And to make matters worse, earthlings are now being charged rent. They must borrow money at usurious rates to pay the rent. There is one earthling that is serving as a middleman and making a fortune. And he stands to make even more as earth is IPOd on some intergalactic markets. The earth seems doomed. Luckily, some people fake a disease outbreak, scare off the investors and manage to get the earth back.
The book is a social critique of the excesses of capitalism. The actions performed by aliens are similar to those done by bankers. At the end, they proclaim a modern utopia. The book does get a bit long. At times it ventures off into "pure science fiction" as it deals with extra-terrestrial communication and long range transport, and then switches back to a social commentary focus.
The Faded Sun trilogy includes the novels Kesrith, Shon'jir and Kutath. The books deal with some conflicts in the future space exploration. Humans are one of multiple species involved in diplomatic maneuvers. Others have very different characters. Some can seem to remember anything and find it strange that human have the ability to lie. The books are dominated by political meanderings and seem to move at a very slow pace. Every now and then parts are interesting, but that is the exception rather than the rule.