It sells "all" herbs and/or 1 gem when they're full. Should have more than 16 max gems for the gem selling to commence, so it doesn't interfere with unlocking gem boxes.
Sells all herbs if they're maxed. If you want to use some, just use them while they're not maxed. If gems are maxed, it sells one, but this only fires if the max is over 16, to prevent you from being unable to buy the first gem box.
