If you are lucky enough to live in/visit Canada, or another country with shorter copyright periods (although Canada’s may be going away with the sad renegotiation of NAFTA), then The Maltese Falcon and many (all?) other Dashiell Hammett titles are in the public domain, and you can get them for free from Faded Page, Gutenberg Canada, or other similar websites. If not, then you may be happy to see a legit (Vintage Crime/Black Lizard) version of The Maltese Falcon on sale in the US for only $1.99, which is the least it has been, according to eReaderIQ, in at least a decade. Hammett’s titles are usually pretty expensive in the US, so I’d grab it now if you even think you might want it ?!
Again $1.99 in the US. Links in the OP are still good.
Hammett’s The Thin Man has dropped to $1.99 at KIndle and Kobo US.
Kindle US: https://www.amazon.com/dp/B004GTLVP4
Kobo US: https://www.kobo.com/us/en/ebook/the-thin-man-1
The Maltese Falcon is £2.99 at Kindle UK right now: https://www.amazon.co.uk/dp/B00N20V112
Red Harvest is the first of Dashiell Hammett’s Continental Op books. It’s £2.99 at Kindle UK right now: https://www.amazon.co.uk/dp/B00MW23DL2