Question: Which brand of root beer has the lowest unit profit available to wholesalers? Indicate the ID of the customer that has the highest number of purchases of the said brand.
SQL: SELECT T3.BrandName, T2.CustomerID FROM rootbeer AS T1 INNER JOIN `transaction` AS T2 ON T1.RootBeerID = T2.RootBeerID INNER JOIN rootbeerbrand AS T3 ON T1.BrandID = T3.BrandID GROUP BY T3.BrandID ORDER BY T3.CurrentRetailPrice - T3.WholesaleCost, COUNT(T1.BrandID) DESC LIMIT 1