How does merging results from multiple search engines affect organic rankings?

Merging results from multiple search engines can definitely mess with organic rankings, mostly by making duplicate detection and canonicalization tougher. Google tries to pick a single canonical URL for each piece of content, but when results are pulled from different indexes or sources, it increases the odds of duplicate or near-duplicate pages slipping through or confusing the system. You might see more clustering of similar results (like indented results or filtering) or sometimes unexpected URLs ranking higher if Google thinks they're the main source. If you're running meta search or aggregating, make sure you handle deduping and canonicalizing before feeding results to users or Googlebot, or you risk diluting your own rankings or sending mixed signals.