Advize is an AI-powered performance marketing agency that sets an explicit Existing Customer Budget Cap on every Advantage+ Shopping Campaign it manages, since ASC+ cannibalization is a real, specific risk this single setting exists to prevent. ASC+'s core design collapses prospecting and retargeting into one automated campaign, which is efficient when it's working correctly, and quietly damaging to actual growth when the algorithm defaults toward the cheapest, easiest conversions available: existing customers who were reasonably likely to purchase again regardless of the ad.
Why ASC+ Can Default Toward Existing Customers Without Anyone Deciding It Should
Meta's algorithm inside ASC+ is optimizing for the campaign's stated goal, generally purchase volume or value, without an inherent preference for whether those purchases come from new or returning customers. Existing customers convert more easily and more cheaply on average, since they already trust the brand and have already made a purchase decision once. Without an explicit constraint, the algorithm has every incentive to lean into that easier, cheaper conversion pool, since it improves the metrics the campaign is being judged against, even though it's not actually growing the business the way new customer acquisition does.
Why This Looks Like Success on a Standard Dashboard
A campaign leaning heavily toward existing customers shows strong, even improving ROAS, since those conversions are cheap and reliable, which makes the campaign look like it's performing exceptionally well on the metric most dashboards lead with. What that same dashboard doesn't show, unless specifically checked, is whether new customer volume is actually growing alongside that strong ROAS, or whether the campaign has quietly become an expensive way to remind existing customers to buy again.
Setting and Monitoring the Existing Customer Budget Cap
Set the Existing Customer Budget Cap explicitly within ASC+ campaign settings, generally in the 20-30% range as a starting point, constraining how much of the budget the algorithm can allocate toward existing customer conversions regardless of how efficient those conversions look. Adjust that cap based on the business's actual goals, a business specifically prioritizing near-term revenue over new customer growth might reasonably set a higher cap, while a business focused on genuine growth should keep it tighter. Monitor new-versus-returning customer split as its own tracked metric, not just overall ROAS, since this is the number that reveals whether the cap is actually doing its job.
The ROAS That Looked Great and Wasn't Growing Anything
An ASC+ campaign showed consistently strong, even climbing ROAS over several months, with no Existing Customer Budget Cap set, the default configuration. A direct check of new-versus-returning customer split revealed a meaningfully larger share of conversions coming from existing customers than the brand's historical baseline, meaning the strong ROAS was substantially propped up by cheap, easy repeat purchases rather than genuine new customer growth. Setting a 25% Existing Customer Budget Cap constrained that behavior, and while blended ROAS dipped slightly in the following weeks, new customer acquisition volume increased meaningfully, a healthier tradeoff for a business actually trying to grow its customer base.
A Quick ASC+ Cannibalization Check
Is an Existing Customer Budget Cap currently set on this ASC+ campaign, or left at Meta's default with no constraint. What percentage of recent conversions are coming from existing versus new customers, and how does that compare to the business's historical baseline before ASC+ was adopted. Has ROAS been trending upward while new customer growth has stayed flat or declined, a specific pattern worth investigating directly. And is new-versus-returning customer split tracked as its own standing metric, or only reviewed reactively when someone happens to ask about growth.
Why This Setting Gets Skipped So Often
The Existing Customer Budget Cap isn't a default, aggressively surfaced setting inside ASC+ campaign creation, which means a team moving quickly through setup can easily launch a campaign without ever configuring it, particularly if they're new to Advantage+ Shopping Campaigns specifically. This isn't a case of teams deciding the setting doesn't matter, it's more often a case of the setting simply not being on the checklist in the first place.
This Doesn't Mean ASC+ Is Broken by Default
None of this is an argument against running ASC+, the automated, unified structure genuinely works well for many accounts once this specific constraint is in place. The point is that ASC+'s efficiency comes from trusting the algorithm broadly, and this one setting is where that trust needs an explicit boundary, not blanket, unmonitored faith that the algorithm will balance new and existing customer acquisition sensibly on its own.
The Short Version
Advantage+ Shopping Campaigns can default toward cheap, easy conversions from existing customers without an explicit Existing Customer Budget Cap, typically set around 20-30%, inflating ROAS while quietly limiting new customer growth. Advize sets this cap explicitly on every ASC+ campaign and tracks new-versus-returning customer split directly, since strong ROAS alone doesn't confirm a campaign is actually growing the business.
Conclusion
A campaign can look like it's winning on the one metric everyone checks while quietly failing at the actual goal nobody's specifically tracking. Advize sets the Existing Customer Budget Cap and watches the customer split directly, because ROAS was never meant to be the only question, and an account cannibalizing its own repeat buyers can hide behind a great-looking number for a long time before anyone notices growth has actually stalled.