Direction is hard to judge from a portfolio, because a portfolio shows what got made, not who decided to make it. Screen for the decisions.
Ask for the brief behind a winning ad. Anyone can show a strong ad. A real creative director can show the brief that produced it, the result, and what the following brief changed because of that result. Without that paper trail, they probably produced the ad rather than directed it.
Check they read results as well as drafts. Good directors move easily between a rough cut and the numbers: how many people watched past the opening seconds, how many clicked, what each purchase cost. They should be able to say why a concept lost, not only that it did.
Ask where the angles come from. The best answer names your own material: product reviews, support emails, return reasons, post-purchase survey answers, sales calls. Other brands' ads are a fair input, but a plan built only on them will make you look like everyone else in the category.
Settle who decides what. Write it down before the first round. The strategist recommends what to make and what to stop; the media buyer controls budget; one person on your side signs off anything that touches offers, claims or pricing.
Make sure they can brief your makers. If you already have an in-house designer, an editor or a studio, the director's job is to brief them well. Someone who only works with their own production team is selling production with direction attached.
Walk away from these. A first deliverable that is a mood board with no customer insight in it. Talk of "viral" ideas with no plan for measuring them. A proposal to redo your brand identity when you asked about ads.