Services for Sale are services that the business sells but are not purchased thus normally, under Accounting tab in the item record only Income Account field can be found as an account related to the item.
When a Transaction Saved Search is created thru Lists> Searches> Saved Searches> New and the criteria is set to any transaction type such as estimate, opportunity, sales order or invoices. The quantity related to the service item for sale shows a negative balance instead of a positive one. Also the related values show negative balances, such as the amount and estimated extended cost. Considering that the item has a positive selling price or positive defined cost.
The problem could be caused by the account selected in the Income Account of the service item, if the account selected in that field is an account whose normal balance is a DEBIT (asset or expense) the quantity that will be reflected is negative since an income account's normal balance is a CREDIT. To correct this, the account has to be changed but one must take note that changing the account in an item record has a retroactive.