Cost on the item screen is for reference only. You have to actually use that item on a purchase and enter the purchase amount for the cost of the item to post to your accounting
PO's, estimates are non posting, they are basically memos of what is ordered or promised
flat rate items, I prefer to use other charge type items, set the amount in the rate block. You can do it flat rate for one hour, and if something takes longer, just increase the qty to 1.5 hours or something on the invoice or sales receipt
What you put on the customer invoice is up to you, but if you carry inventory you can not show it being used easily without putting it on a sales form, you can "sell" inventory for a zero dollar amount and still have the correct accounting for qty on hand and cost. The flat rate item would indicate the sale price in this case
Personally I would put each item on the customer sales receipt with a zero dollar sales price, so that there is record of what exactly I worked on in case the end item comes back to you, and for work warranty issues.
