Run the arithmetic first: a specialist worth hiring costs $300–$1,000+/month at small scale. On a $1,000/month ad budget, management fees are 30–100% overhead. At that size, learning the weekly search-terms ritual yourself usually beats paying it. Above roughly $3,000/month in spend, a good specialist typically recovers their fee in eliminated waste.
If you do hire: the first conversation is the tell. A specialist who asks about your conversion tracking, margins, and close rate before touching keywords is doing the job; one who quotes a management fee before asking what a customer is worth to you is selling a subscription.
Either way, the account lives under YOUR login and they get manager access. Never the reverse. That rule has no exceptions.