The items you purchase from the wandering merchant aren’t purchase locked, even when you only need 1 of the items they can be purchased indefinitely.
These items are untradeable and cannot be dismantled.
There are quite a few posts on the forum regarding this, where people (including myself) have lost all their silver by buying out the MAX number of items. I understand this this is due to our own mistake. However to be fair, there’s no reason for anyone to need to be able to buy infinite untradeable items when you only need 1.
In my case I was rushing to buy the item as the merchant was about to disappear so I hurriedly bought the MAX items. 9 mil silver gone.
I think a good solution for this would be if we could sell these items back at a merchant/shop at their original price.