Some ideas for you to (ok) chew on:

How can you make the shop owner more of a celebrity for letting
your vening machine sit in his/her store?


Can the candy be co-branded in some way so the shop owners gets to say it's their candy too?

Can you setup competition so that the store that sells the most candy each month gets a free radio spot on the local radio station

Those vending machines thart aren't doing well can you instead offer a deal to the owners of shops where they are doing well a joint venture.

Let that shop owner make inquiry to his network of business owners to get a placement and give him a sweet deal for it, 80/20 something like that.

He's/She's doing work for you and they are motivated to find a good spot since they get a cut. You with no leg work have a chance to have a better performing vending machine.