As per the survey by Statista in the UK and the US, the market for second-hand books grows yearly at an average of 8 to 10 per cent.
Some of the rarest ones, which are not older than 20 years but are still very expensive, like the first edition of JK Rowling's books -
The Tales of Beedle the Bard, which was a leather-bound book and can be resold in the range of $300 to $10,000, or any signed copy of JK Rowling's book, which was published in 1998 or 2000 are surprisingly valuable and includes rare children and comic books.
Comic books, from the last two decades, are considered valuable where the value of some bought for a few dollars is over $100 on resale.
Those interested in book collection should seek alternative sellers, not just Amazon.
Some of the features of the books should be carefully examined. A Penguin version is mostly considered long-lived, as many from the 1930s are still in demand.
If you suspect it is a valuable book, get it appraised by an expert to know the real value of the book.
The books written by famous authors and those published in the last centuries may not become popular even if they are rare but not in good condition.
The desirability for certain books is unpredictable, and plenty of books may be cheap or worthless, especially those with thousands of copies in the market.
Some are copies of books that may have a higher market value, like Apple's first manual or Superman comic.
The book of 1896 by Kelmscott Chaucer, which had only 400 copies, was put on AbeBooks for $137,500.
Collecting even some of the comic books with all the editions in one place can get a higher value, and the ones with specific printing mistakes in some editions can be rare and desirable.
The age of the book matters where the Fellowship copies, which were released in 1954, can be extreme outliners like the First American edition, which is most sought after.
The ones printed in the 14th or 15th century have great historical values associated with the era.
Many rare books bought by museums and high net-worth buyers were printed before 1801.
The book's condition should be good, even if it comes from the 14th century. The ones with torn pages or scuffs or marks can lower the book's overall value.
Pages should not deteriorate to the extent that it is difficult to handle and store the book for long.
Since several rare books are bought for thousands of dollars, buyers seek proper condition with low damage.
The ones with hardcover are easy to store, and paperback books may require extra care & storage expenses.
Overall investment in such items is associated with a passion for reading, and it's necessary to get associated with libraries, booksellers, or experts who have read and collected several books.