Adequate action taken for noncompliance with the service level agreement (SLA) provides the best evidence that outsourced provider services are being properly managed. This shows that the organization is monitoring the performance of the provider and enforcing the terms of the SLA.

The other options are not as convincing as evidence of proper management. Option A, the SLA includes penalties for non-performance, is a good practice but does not guarantee that the penalties are actually applied or that the performance is satisfactory. Option C, the vendor provides historical data to demonstrate its performance, is not reliable because the data may be biased or inaccurate. Option D, internal performance standards align with corporate strategy, is irrelevant to the question of outsourced provider management.