So .. outside of just buying some stuff, is there something else you are supposed to do here? Or there are just things that are for sale and it's different every day?

Thanks in advance :)

Are you talking about Ujin? He has 3 items a day from his stock and it can be months before items appear again. If you are looking for any of his stock it is definitely worthwhile to check every day!

Thanks Rogue!

I'm just buying whatever he has everyday and chucking it in my vault lol.