Spent the last stretch building Shopify themes and reviewing dozens of stores, and the pattern is always the same: founders pick a theme based on how it looks on desktop, then wonder why mobile conversion is half of desktop.

Three things kill mobile conversion almost every time:

1. The add-to-cart button isn't sticky. If a buyer has to scroll back up to find "Add to Cart" after reading specs, you've already lost a chunk of them. A persistent bottom bar with price + button visible at all times is non-negotiable for anything above a $30 AOV.

2. Upsells are bolted on with an app instead of built into the template. Every extra app is another script tag slowing down your Core Web Vitals (and Shopify does penalize slow themes in organic reach). Native section-based upsell blocks load faster and look like part of the page, not a popup fighting for attention.

3. No trust signals above the fold on mobile. Desktop has room for reviews, badges, and guarantees near the buy box. Mobile compresses everything — most themes just... drop them. That's the exact moment a first-time buyer is deciding whether to trust a store they've never heard of.

None of this requires a developer or a rebuild. It requires a theme built OS 2.0-native with these as actual sections, not afterthoughts. Happy to answer questions if anyone's mid-redesign and stuck on this.