A flat ACoS doesn't mean your agency is doing a good job

A stable ACoS on the dashboard doesn't actually tell you whether an agency is growing the account or just holding a number steady.

Better signal is TACoS, ad spend over total sales, and whether it's compressing over time as organic sales pick up the slack from SEO work. Second is whether the brand is gaining real category share, concentrating volume into a key ASIN strong enough to earn Best Seller badge status rather than spreading thin across too many listings. Third is whether bid and budget decisions are actually synced to real FBA stock levels in Manage All Inventory, instead of pushing spend on a product that's about to go out of stock.

A flat ACoS with none of these three moving usually means the account is being maintained, not grown.