Yes

But it's a common business model. That's how amazon makes money (they can do all their discounts because they sell such huge numbers that they don't have to make a big profit on each book). I suspect it was Fopp's business model (okay it went bust, but because of expansion problems not because of that approach).
The reason it seems to make sense is that I know second-hand bookshops get most of their books very cheaply in house clearance sales and so on. Which would seem to lend itself to a high volume, low mark-up approach. But there probably are reasons it doesn't happen.