The nervous question behind every bundle: "am I just giving 25% off to people who'd have paid full price?" Sometimes, yes. The framework for thinking clearly about it fits in three buyer types.
The would-have-bought-everything buyer is pure cannibalization: they'd have paid $18 across the year; now they pay $13.50 once. You lose the discount, minus the fee saving. These buyers exist but are rarer than sellers fear — buying five things one at a time requires five separate moments of conviction, and most people never complete the series.
The would-have-bought-one buyer is where bundles earn their keep: they came for the $4.50 unit-one pack, saw the whole-unit bundle for $13.50, and tripled their order. Cannibalization of $4.50; upsell of $9. This is the modal bundle sale in most stores, and it's why average order value, not per-item margin, is the number bundles move.
The would-have-bought-nothing buyer is free money: the bundle's crossed-out price and completeness ("the whole year, sorted") convinced someone a single item never would. No cannibalization at all.
You can't survey buyers, but two signals approximate the mix. If bundle buyers' order histories (visible in your sales data) show prior individual purchases from the same series, cannibalization is real — consider a smaller discount. If bundles sell to fresh buyers, they're doing acquisition, and the discount is your marketing budget. And watch the series' individual sales after launching a bundle: a modest dip with a larger bundle rise is the healthy pattern; individual sales collapsing to zero suggests the bundle per-item price has undercut the singles too aggressively.
Bundles are a bet that completeness and a visible saving create purchases that wouldn't otherwise happen. It's usually a good bet — but it's checkable, and your sales data will tell you within a term. Price the bundle so a type-one buyer doesn't hurt too much, and let types two and three pay for the experiment.
General guidance, August 2026. Not affiliated with TPT. Not financial advice.