Get negative Values in 0UC_SALES_STATS_01 or 0UC_SALES_STATS_02
If you transfere billing line items into Sales Statistic, you have line items where the sign of the quantity is negative, even you see it positiv in your billing document.
The sign of a quantitiy is following the sign of the amount of each line item. If the amount is zero the sign of the quantity is determined from the Subtransaction.
If this system behavior does not match your thoughts you can change it via customer extension EBIA0001 --> EXIT_SAPLEA16JELP_002. For more Details you can check Knowledge Base Article 1537193.