Final answer:
Shareen is employing the influence tactic of scarcity to persuade Chantel to buy the puppy by suggesting its availability is limited.
Step-by-step explanation:
Shareen is using the weapon of influence known as scarcity to try to motivate Chantel to purchase the puppy. The concept of scarcity is based on the idea that people are more driven to value and desire something when it is perceived as rare or in limited supply.
In this case, Shareen implies that the opportunity to buy the puppy is scarce because another family is interested, which may prompt Chantel to make a decision more quickly to avoid losing the chance to purchase the puppy.