What is the bidding behavior of a Performance Max campaign versus a standard shopping campaign when serving identical products?

When serving identical products, Performance Max campaigns and standard Shopping campaigns exhibit distinct bidding behaviors. Standard Shopping campaigns provide granular control over bidding strategies, allowing you to set manual bids, enhanced CPC, target ROAS, or maximize clicks, primarily within the Google Shopping network. You control keyword targeting and negative keywords to influence which searches trigger your ads. Performance Max campaigns, on the other hand, utilize automated bidding across all Google advertising channels (Search, Display, YouTube, Gmail, Discover). Performance Max prioritizes conversions and ROAS (Return on Ad Spend) by leveraging machine learning to optimize bids in real-time based on user signals, audience data, and conversion goals. If both campaign types target the same products, Performance Max will typically outbid standard Shopping campaigns when it predicts a higher probability of conversion, even if the initial cost per click is higher. This is because Performance Max considers the full customer journey across multiple channels, whereas standard Shopping is primarily focused on search queries. This can lead to higher overall spend and potentially higher ROAS with Performance Max, but less direct control over individual bids and keyword performance. Performance Max also uses audience signals to find new converting customers whereas standard shopping is limited to search terms.