Custom report for items which sold on low margin

Dear all,
Kindly help me to guide on how to create custom report on inventory margin less then 10% or negative margin.
some times while entering sales, my team makes mistake in prices. so is there any way to prevent sales entry to be posted if sales value is less then cost ? or any way to make a custom report where admin can run the report and we can see, which sales has less then “10%” or negative margins ?

Please read the Forum’s FAQ/Rules, especially where it says:

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Why not use the Inventory Margin Report? You will not be able to get this information from a custom report, because margin is not a transaction variable.