Performance Max doesn’t run on keywords the way Search campaigns do it runs almost entirely on your Shopify product feed, which means the campaign is only as good as the data feeding it. Vague titles, missing GTINs, or thin product descriptions don’t just hurt SEO on the storefront, they starve PMax of the signals it needs to match products to the right shopping queries, often quietly capping ROAS without any obvious error in the account. Custom labels become the real lever here segmenting the feed by margin, bestseller status, or inventory level lets budget get steered toward products that are actually profitable to sell, instead of PMax defaulting to whatever converts most often regardless of margin. Attribution adds another layer of risk: PMax pulls in Search, Shopping, Display, and YouTube inventory under one campaign, which makes it easy to overcredit paid spend for sales that would’ve converted anyway a problem that only shows up when ad performance is reconciled against actual conversion rate and on-site behavior. And because PMax optimizes toward whatever a Shopify pixel tells it counts as a conversion, that signal needs to be clean from the start new customer acquisition and returning buyers driven by email and SMS flows shouldn’t be counted as fresh ad-driven revenue, or the algorithm ends up optimizing for the wrong outcome entirely.