It's true in a sense that an instrument made in a humid climate can come to a dryer one and crack.

But... if you're buying direct, you can easily avoid any issues by slowly acclimatizing it to the new location.

What's a humidifier cost? If it's in the middle of your giant living room, then it's not really practical, but if it's in a music room, crank the humidifier and slowly back it down over the course of a week. The wood will settle and you're all set, you won't have to worry about it again.

It's really not that big of a deal, it's not a myth, but not the horror story some make it out to be.

I buy ( too many ) guitars, and as much as I'm dying to open the case and play it, I let it sit in my house for a couple days in the case and she's perfect ever time.

Woods will condition themselves to the climate, they don't prefer one or the other, the transition between the two extremes is the only worry.