Were they using a non-invasive meter or a pin meter for the mc tests? To me 30% sounds a little odd like they used a non-invasive meter. Next inspector that comes out...ask if they ever have installed hardwood for a living. lol
Typically a huge percentage never have and rely on manufacturers biased triaining. Thats all they know.
Cracks/checking outa the box usually means low mc. Installers should not be responsible for mositure issues after the fact as they can change in a matter of several days unless preventitive steps were taken, and if you objected due to the cost it's your fault.