Anyone COULD/CAN tell

Hello dear Helpers,

I have another problem with “can” and “could.”  I’m reading a text and I don’t understand why the author uses “could” instead of “can.”

Here is the text:
We finished Pride and Prejudice and turned to Great Expectations. My mother thought Pip’s admiration for Estella was unconvincing. “It’s the weak link in just about every book I’ve ever read,” she said one day, lying on the couch with the book on her lap, her raspy breathing punctuated with a barking cough. “They set up a very smart, very thoughtful, very nice character, and then have him fall in love with someone that anyone COULD tell is a horrible human being.”

I would replace “could” with “can.”  Please, explain me why the author use “could.”

Thank you very much,

Spoonfedbaby

The author used "could" to stand for the conditional  structure (consequent clause) "would be able".
The author felt that there was an implicit condition "if they were paying attention to the development of the characters (in the narrative)".
" ... and then fall in love with someone that anyone, if that person were paying attention, would be able to tell ..."

"can tell" is a rather unconditional expression in comparison.

CJ