Work
Let me try this a different way.
Suppose you grossed $X per month from your
vending machine with it carrying ..... pick a number ..... 30 items. Now, expand that to 51 items and suppose you gross an additional 5%. Is it worth it to *you* to make an additional 5% by having to order, store, and restock another 21 items? For me, it is not; for you, perhaps it is. It's not about being lazy or not wanting to make money.
Personally, I don't have the room in the equipment room at the car wash to stock all the vendor stuff. Not even close. So it takes up an entire large table in a spare bedroom. After all, since shipping fees substantially increase the cost per vend item and you focus on profits you *will* order in large quantities to save on shipping, right? Then I lug a "restock kit" from the house down to the wash to re-fill the vendor. For me, doing it with 18 items is one thing; doing it with 51 would be much different. (Actually I only sell about a dozen items as 5 rows are devoted just to towels.)
Bottom line: I don't think expanding the number of items in my vendor will expand the revenue derived in any way that justifies my time to handle the increased ..... stuff. Your mileage may vary.