Relevant article:
What do they do with all the other copies they get?
I think they only get one copy of each title/edition/ISBN number unless that first copy is defective and can’t be scanned. Remember there are tens of millions of those published.
More likely they just scan them all and let God the Computer sort it out. At the scale they’re working at, it’s probably more trouble than it’s worth to have any sort of process for ensuring lack of duplicates.
Their website presents a very different view: “Books Belong With Readers”
At Zoom Books, we believe every book deserves a second life. As a leading book recycling and donation company serving Canada and the United States, we use smart logistics and a deep commitment to sustainability to acquire, sort, and resell over 2 million books monthly—connecting stories with new readers and keeping waste out of landfills.
Sounds like they were founded with good intentions and green goals. It’s possible they have adopted a new strategy to build AI datasets.
Or maybe they’re just lying. That’s always possible, too.
Yes, Google once also claimed to “do no evil”, and see where this has led us to.
Google signaled they had changed course by dropping that slogan. 
I’m sure they did some evil before that, but i heard an interview of their CEO on NPR years ago, when it was still their official align, and he said they had decided against several initiatives because of that slogan. I guess at some point they decided it was costing them too much.