I don't understand the reasoning of locking a bunch of unique items in a merchant you can only access, at most, once a day.
To make it worse, it is the only place (as far as I know) to convert MSP stones to their higher tiers.
Why? Why do I have to run between MSP and CS like that? Except I can't even do that since I'm locked out of CS after once a day there..
So let's say, for example, a player wants to buy a VT soul-shield piece with verdant stones. Since they have thousands of them;
Go into MSP, check the price of the piece you need, leave and get (hopefully) what you need from vault.
Now get a party and beat Cold Storage 1st boss. If they happen to do 2nd boss they may not wait for you, so you either give up on joining them and forfeit the reward, or join and wait another whole day to get access to the merchant, though the same Kaari Lord boss issue may happen again the next day.
Once at the merchant, hope you have all you need to convert the currencies (solar energies? Demon spirit stones? Crystals?), because if you don't have it on you and you're not premium, you'll have to wait another whole day since you can't access vault there.
Finally got what you need and got enough yellow stones. Go back to MSP, buy the piece and hope you got that good roll on it. No? better go back to Cold Storage.. oh wait, it's locked for the day…
This problem applies for other stuff at that merchant, mainly, the unity stones and keys.
I got a little petty here, but I think you get the point. It is just so silly, and I don't think it helps in selling resets, if that's the reason.