Which of the following people are practicing concealment?

Mandy's misrepresentation about the age of her roof constitutes a form of concealment, but it is not the only example here. While it is deceptive, it pertains specifically to the condition of the property rather than a significant change in occupancy status, which is a more critical factor in insurance terms.

Charlie's discrepancy regarding mileage is indeed a misleading statement and could potentially impact his premium. However, it does not involve the same level of concealment regarding occupancy or usage of the property as Joey's situation, which directly affects the insurer's risk assessment related to vacancy.

Bonnie's action is a clear example of misrepresentation aimed at obtaining a better rate. Nevertheless, it does not relate to the concealment of material facts concerning property usage or occupancy, which is crucial for evaluating insurance risks.