Answers
How big does an audience list need to be?
Big enough for Google to serve it — a few thousand for most list types.
The short answer
Big enough for Google to serve it — a few thousand for most list types.
Below the minimum, the audience simply will not serve and the campaign looks broken when it is only empty.
Small stores usually do better with broader targeting plus a strong offer than with tiny, precisely-defined lists that never reach anyone.
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