Rate from my vendor bill doesn't add up to inventory cost under Product/ Services. How to connect rate to inventory cost? Should I manually change cost every time?

Jen_D said
Currently, updating the item rate on your bill does not update the original cost in the Products and Services.
Of course it does, the rate on the bill is how inventory items get the cost per item per purchase.

For you to add a new value, you'll need to edit your inventory items one at a time.
You do NOT adjust item value, and in QBO you can not do that anyway

 @sezin

The cost you see per item in QBO reporting is not always correct, QBO inventory reporting is terrible.

QBO keeps FIFO inventory which is average cost per purchase.  When you sell an item the cost of the item sold is the first cost for that item and qty that was purchased.  ie

buy
widget, qty=3, $1.00 ea
widget, qty 10, $0.75 ea

Sell 5 each, the cost is
3 at $1, = $3
plus
2 at 0.75 = $1.50
total posted to cogs is $4.50

That $4.50 in cost will only show up in a transaction journal for the sale, and the detail posting in the COGS account, but you will never see that amount as item cost in any QBO inventory reports