"Modern, 20th-century encyclopaedias really aren't worth anything at all now," rare book dealer Derek McDonnell told ABC Radio Perth.
Second-hand book dealers cannot sell them, and even some charity shops now decline them as donations, he said.
Yet encyclopaedias were once a part of every home that could afford them.
Before the internet, they were also the only way that individuals could readily look up general information.
"There was always that special shelf where the knowledge was shelved and you went to it when you had homework," Mr McDonnell recalled.
"Some of them were sold door to door, and some of them were sold in parts; you became a subscriber and a bit more would arrive each month.
"Alternatively, you would buy the whole thing in one go and it was a massive investment, around $800 to $900 at the time."
Internet encyclopaedia Wikipedia celebrated its 16th birthday this week, and while it has completely supplanted the printed encyclopaedia industry, Mr McDonnell pointed out it was simply the latest iteration of a tradition started 2,000 years ago.
"It's a great time to celebrate what Wikipedia has done, because they have completed a process that started in the 1st century when people tried to organise knowledge.
"The 1st century is when Pliny, the Roman, published his natural history, Historia Naturalis, in which he tried to bring together all the information on the natural world."
'Great for settling arguments'
Despite their obsolescence, many people still have fond memories of encyclopaedias.
"I'm 58 now and can still remember the door-to-door salesman selling my parents a set of Colliers Encyclopaedia in the late '60s," Jack told ABC Radio Perth.
"They were great for settling arguments in the day ... they now rest at my place, I just couldn't bear to see them thrown out."
"I bought the World Book encyclopaedia set from a salesman at the door in the '70s," Karen recalled.
"We did refer to them for 30 years, till Mr Google came along."
Others have found alternative uses for theirs, like Ruth, who said she used three volumes to prop up her furniture.
"Volumes C-Z are propping up an Ikea cupboard I didn't make particularly well in my front room," she wrote.
Mr McDonnell said: "It's sad because they were big investments, but that moment has passed and Wikipedia has completely superseded what they did."