Rather try NOT EXISTS
Something like
INSERT INTO eBayStockTaking (OrderLineItemID,Qty,SKU,SubscriberID,eBayUserID)
SELECT OrderLineItemID,
Qty,
SKU,
SubscriberID,
eBayUserID
FROM tempEBayStockTaking t
WHERE Not EXISTS (
SELECT *
FROM eBayStockTaking e
WHERE e.OrderLineItemID = t.OrderLineItemID
AND e.SubscriberID = t.SubscriberID
AND e.eBayUserID = t.eBayUserID)
)
I know MySQL allows Row Subqueries, nut SQL Server does not allow this.