I wouldn't say it is a scam exactly, but they do certainly get up to the practices you describe. They factor in complaints and having to make refunds etc without checking ... it is part of their business model.
I've just had something similar with another eBay supplier - book paid for and didn't arrive. From looking at their feedback you can see this happens a lot. They just refund without a quibble.
A 'friend of a friend' used to work at World of Books in Worthing. I understand that (as you might expect) conditions and pay are pretty poor there...