Explanation
According to this source, if an object is set to Controlled by Parent in its organization-wide default settings, then access to its records is determined by the parent record. In this case, since Case object has View All permission for service reps, they will be able to access all contact records related to those cases, regardless of their ownership or sharing rules. However, they will not be able to access all account records, since account object has Private OWD and no other sharing mechanism is mentioned. The other options are not correct.

Explanation
To improve performance when a dummy user owns more than 10,000 lead records, it is recommended to assign ownership to a small number of users and do not assign a role to the dummy user. Assigning ownership to a small number of users reduces the number of sharing calculations and recalculations that occur when role hierarchy changes. Not assigning a role to the dummy user prevents the dummy user from granting access to other users in the role hierarchy

Explanation
The best way to review access to a certain set of key customer accounts is to export the Account Share table and review it. The Account Share table stores all the sharing records that grant access to accounts, including manual sharing, sharing rules, team sharing, and implicit sharing4. The other options are either not feasible or not comprehensive.

Explanation
A sharing rule is missing to share Accounts to the AR team, which could be the issue preventing AR team members from seeing invoices. Since invoice is a custom object with a master-detail relationship to account, its sharing settings are controlled by its parent account. If AR users do not have access to account records, they will not be able to see or query invoice records either. Option A is incorrect, since a sharing rule to share invoices to the AR team would not work, as invoice inherits its sharing settings from account. Option B is incorrect, since assigning an invoice page layout to the AR team profile would not affect their visibility of invoice records. Option D is incorrect, since giving read permission to the invoice object to the Accounts receivable profile would not grant access to invoice records that are owned by other users.