There appears to be a bug in the 1.3 beta. You can buy an iridium sprinkler on Friday and it disappears from his inventory. But once you close out and then open back up, the iridium sprinkler is back and available for purchase.
:1.3.10 was pushed today - try updating the game and see if you can replicate the bug. If so, you should report it on the Chucklefish forums: https://community.playstarbound.com/threads/stardew-valley-multiplayer-beta-known-issues-fixes.142850/ --[[User:Margotbean|margotbean]] ([[User talk:Margotbean|talk]]) 16:58, 9 May 2018 (BST)