What an agency does well
A good agency brings strategy, category experience, creative for Sponsored Brands, and a human to talk to. For a launch, a brand repositioning or a complex catalogue, that judgement is worth paying for.
What it actually costs
The common model is a monthly retainer plus a percentage of your ad spend (often a few to ten-plus percent). That means your cost rises every time your spend does — even though the daily work does not get harder. On a large budget, the commission alone can dwarf a software fee.
The daily work is rules-driven
Strip out strategy and most of what happens day to day is mechanical: trim losers, fund winners, block waste, watch the budget. That is exactly what automation does well and consistently — see the honest comparison on AIAdKing vs an ads agency.
A practical decision rule
If you mainly need consistent daily execution at a predictable cost, software like AIAdKing usually wins — flat fee, no commission, every change logged. If you need strategy and creative and have the margin for it, an agency (or a consultant for direction plus software for execution) can be worth it. Many sellers start with automation and add human help only where it pays back.