Counting unique records across 2 columns and computing a score based on boolean values
This would be very simple in SQL. As far as I can read the BigQuery Query reference, it supports all (GROUP BY clause, COUNT() and SUM() functions, CASE expressions):

SELECT 
    custID, InteractionDate,
    1.0 * COUNT(CASE WHEN Purchased = 'T' THEN 1 END) / COUNT(*) AS Success,
    SUM(Sales) AS Sales
FROM
    tableName
GROUP BY
    custID, InteractionDate ;