Two things. First of all, apples are only available at harvest. In that system he could only buy things once a year, because his apples have a limited shelf life. Second, even if he did have the apples on hand, it's still credit. If you take the note to him, how do you know the apples will still be there? How do you know they will be as advertised? How do you know he will honor the note even if he's got the apples?