It isn't - deprecation of held goods is always a risk and if you're working on consignment then that comes with weird financial liabilities. If there's a flood and you lose your inventory it sucks - if there's a flood and you lose an inventory of consigned values then suddenly you're potentially exposed to paying market value for a number of items in addition to all the site damage you'll need to address. Capacity is one aspect of the costs of holding inventory - but breakage is the much more expensive consideration and consignment just makes it even more expensive.
a large part of the value of secondhand stuff is in the box and packaging, assuming those nice boxes in the image were from his collection - those are a little more fragile than the Lego pieces themselves.
Edit: wait, the whole collection was sealed and new in box. Yea, just water damage to those boxes would cut the value by at least 10%. Collectors are picky as shit.
They were sealed in box? Yeah you'd be right that damage would be easy and could significantly reduce the value.
I didn't realize people bought Lego to leave in the box. But I guess I shouldn't be surprised because it's a common thing for collectors to do in other hobbies.
Even without the box I think you're underestimating how damaging water is. If you're experience a flood it's never distilled H20, sometimes it's sewage and that's just awful, but even if it's storm water or a broken water main the water isn't the difficult portion (though that alone can lead to all sorts of mold issues) it's the sediment. If that sediment is from brown water there are obvious biological hazards which may lead to destruction being the only economical resolution, but even if it's just mud and sand that forces a huge expenditure to actually clean the products and if there's a signficantly misaligned pH it may damage products that you otherwise think of as water resistant.
Given this was a set of full star wars legos with decades of age a lot of those bricks are already going to have degraded somewhat and technix style components are likely to be significantly damaged from internal sediment accumulation. If you drop your water proofed water in a stagnant pond for three weeks it's likely that the internal seal will hold up and protect the delicate components but you'll probably need someone to pull the glue or other sealant out and replace it as well as going over the exterior surface with cleaning solutions to get it back to the quality it was in before being submerged - and flooding is rarely an instantaneous affair.
I wouldn't underestimate just how damaging to goods storage can be - and if you're doing it at scale you're going to be paying that cost constantly just as a percentage of value stored.
Lego survives being eaten by babies and poop back out again (source: my younger brother). They also survive being left out at theme parks (ie the various Legolands) and primary schools under all weather conditions for months and years.
So I don't think I'm underestimating the resilience of Lego bricks to flooding.
There was an article a on HN a while back about the plastics chosen by Lego. They put an exceptional amount of time and effort into choosing durable materials for their bricks.
Only tangentially related, there was a "500-year" flood in my region a couple of years ago and a manager in my department who would shortly become the company president had his house flood. I volunteered to help with cleanup and ended up at his house tearing his basement, at one point 8' under water, down to the studs. His near-adult kids had small Lego collections that were basically in untouched condition except they had been under water. He told us to throw them out with everything else - it was not worth the complicated effort to do them and sort them out. But out of all the stuff it took us the most convincing to do so, the bricks weren't damaged at all.
That said, I'm surprised Lego survive outdoors. My understanding is that ABS is not UV-resistant.
I believe in this case the consignment contract requires the store to hold insurance on the consigned merchandise, which I assume is intended to address this concern.
