I'm going to suggest you discuss this with the seller, as I have a several year history with him, and have been surprised and pleased with every stone so far, 5 if I remember correctly.

If there is a crack that is making the stone unusable, the sooner you tell him the sooner he can seek a replacement. I have bought a vintage Aoto from him after I'd purchased one elsewhere that was 'gritty' and borderline useable, and he delivered an UGLY old doorstop of an aoto that sharpens like a dream.

One thing to consider, the relative value of our currency vs yen has made prices in dollars go up 50% in the last 2 years. If you want quality, bring money.

My largest hone cost < $400 3 years ago, and I suspect over double that now, as it improved greatly after I received it. A thin layer flaked off the bottom and exposed a surface equal to the top side, which I lapped and now use regularly.

There aren't many Japanese hones useable on both main flat surfaces, and I've gotten 2 fully useable out of 5. I'm feeling guilty because my good fortune is so different from your experience. You can consider that every stone so far has been a keeper, not for sale, period, at any price. I very much hope you wind up with one that pleases you as much as mine please me.

Talk to him. I think he cares about stones a great deal.