If I update the cost or selling price of a product or service does the new prices affect future sale only or does it affect retrospectives?

It does not work that way, @mshafi@ledgersfi.

Updating the cost or selling price of a product or service in an account does not perform the changes retrospectively. This means your existing accounts and transactions remain the same and it'll only affect your future sales and expenses.

I'm adding this article with tips you can use in managing your business's growth using QuickBooks Online: QuickBooks Help Articles. Click any of the existing boxes to view other product areas such as reports and transactions.

I've got your back if you have additional questions updating your items. I'm always around to help. Take care, and I wish you continued success!