Engagement rate is interactions divided by reach or impressions: what fraction of the people who saw a post did something with it — reacted, commented, shared, saved, or clicked. It began as an organic-content metric, but paid ads have one too, and for advertisers it doubles as an input: Meta's delivery system reads engagement as a signal of how much people want to see an ad, which feeds back into delivery and cost.
The trap is treating engagement rate as a quality score when it is really a quantity score. The metric counts a scam link, a furious complaint, and a "where do I buy this?" identically — one comment each. An ad drowning in comment spam or ratio-style pile-ons can post a spectacular engagement rate while actively repelling customers. The inverse trap exists too: manufacturing interactions with engagement bait inflates the number while Meta's policies push the content's distribution down.
So for paid ads, the useful move is to split the metric into composition, not celebrate the total. What kind of engagement is this? Questions about price, shipping, and sizing are the best kind — each one is a buyer-intent comment, a warm prospect raising a hand on an impression you already paid for. Spam and abuse are engagement you want gone before the next thousand viewers see it. Complaints are engagement that needs a human answer, fast and in public.
That triage — classify every comment, hide the harmful, surface the valuable, answer the rest — is what ad-focused comment moderation does, and it changes what a "high engagement rate" means on your ads: less noise counted, more signal answered. Tools like sentiment analysis and intent classification are what make the split workable at ad-account scale, where popular campaigns generate more comments than any human team can read line by line.