Does a lender's legal duty to get the best price in a power of sale protect me as the buyer in any way?

Not directly, and this is a common point of confusion. A mortgagee exercising power of sale generally owes a duty to take reasonable steps to obtain a fair price reasonably obtainable for the property in the circumstances - but that duty runs to the defaulting borrower and to anyone else with an interest in the proceeds, such as a subordinate mortgagee, not to you as the prospective buyer. Its purpose is to make sure the debtor is not shortchanged by a lender that has little incentive to maximize the sale price once its own debt is covered.

For a buyer, the practical effect is indirect at best: it means the lender is not simply looking to unload the property for the lowest workable number, which can support a reasonably arm's-length process. It does not translate into any representation to you about the property's condition, its value, or the fairness of the specific price you end up paying, and it gives you no direct legal claim if you later feel you overpaid.

Treat this duty as background context about how the sale is conducted, not as a protection you can personally rely on as the purchaser.