Answer:
c. instrumentality
Explanation:
Instrumentality refers to the Quality of being an instrument, Agency or means by which an entity accomplishes its functions or fulfills its obligations, achieves it purpose or gets to a conclusion.
The waiter believes that suggestive selling is not instrumental to the amount of tips she gets.
It can not be proven that by suggesting what a customer buys for him will automatically lead to him or her tipping you while leaving.
Suggestive selling implies trying to suggest to a customer what to buy from a store you own or you are working.