I get that, I really do, and dread to even begin to think what a modern showroom costs to run for a week, let alone build. But WBAC aren't dealers, they're middlemen and I would be willing to bet the majority of the cars they buy are more than 3 years old and there are no prep costs. Staffing, building hire, transport yes, but no expensive showrooms and no come backs when they've been through the block.
Not at all averse to them making money, it'd be a pretty cr*p business that didn't make as much as possible, but they are exceptionally picky in my experience.