Try something like this (check out
HAVING
):
SELECT COUNT(*) AS Cnt,
dbo.Receiving.ManufacturerSerialNumber,
dbo.Receiving.UserId,
dbo.Receiving.WorkCompleted,
dbo.FullRepair.EngineersReportId,
dbo.FullRepair.UserId AS Technician
FROM dbo.Receiving, dbo.FullRepair
WHERE dbo.Receiving.ManufacturerSerialNumber = dbo.FullRepair.ProductSerial
HAVING COUNT(*) > 1;
Good luck!