"take it on the lowest basis"

[imchongjun]

Hello, teachers.
Will you tell me what the phrase "take it on the lowest basis" means in the following passage?
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"You're the guy that calls bookselling the worst business in the world," said Roger warmly, "and you're the kind of guy that makes it so. I suppose you would say that it is no concern of the bookseller to try to increase the public appetite for books?"
"Appetite is too strong a word," said Jerry. "As far as books are concerned the public is barely able to sit up and take a little liquid nourishment. Solid foods don't interest it. If you try to cram roast beef down the gullet of an invalid you'll kill him. Let the public alone, and thank God when it comes round to amputate any of its hard-earned cash."
"Well, take it on the lowest basis," said Roger. "I haven't any facts to go upon----"
"You never have," interjected Jerry.
"But I'd like to bet that the Trade has made more money out of Bryce's American Commonwealth than it ever did out of all Parson Wright's books put together."
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It seems to me that the phrase "take it on the lowest basis" means "look down on the public if you like", but I am not sure if this is the correct interpretation. I appreciate any comments from you.

[Anglika]

Take it at the lowest common denominator - the most sellable books you have.

[imchongjun]

Hello, Anglika.
Thank you for your comment, but I am not sure if I understand your answer. I still don't understand what the whole phrase "take it on the lowest basis" means. This expression is from a novel written in 1919 and seems to me to be old-fashioned and somewhat puzzling. I hope you would elaborate on your comment. Thank you!!
Imchongjun

[Anglika]

This is an argument about what bookselling should be about.

In order to support his argument, "Roger" says that at the lowest basis - which for the purpose of this argument is the amount booksellers have made when selling a book - booksellers have made more from selling copies of Bryce's American Commonwealth [a serious two volume book] than from a popular series.