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.
replyEdit: 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.
replyI 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.