The biggest problem I see for new users of hard Japanese stones is that they do not do enough pre polishing first.
Many claim that their hard stones are not finer than their medium hard stones. But fact is that very hard Jnats are extremely fine and with the first passes will reveal scratches from the previous coarser stones. They tend to leave mirror finish to the blade if not used with slurry and that mirror finish reflects all the scratches that were left from other stones. When using a hard finishing stone in such a manner a person can be mislead to think the stone is not fine, while in fact the person did not spend enough time on the stone.
I was guilty of this when I fist got some of the harder ones, even Kizuyama at Lv 3.
Put the above paragraph somewhere on your store and make sure you have a link to it from harder stone listing