IHTM28140 - Liabilities: investigating liabilities: goods and services
You should only challenge a deduction for goods and services if the deduction claimed is large in relation to the estate as a whole or there is evidence of some inconsistency or avoidance. You should apply the general principles (IHTM28040) of investigating liabilities to these debts.
You should challenge any debts that are clearly disallowable if the amount of tax at stake is worth collecting.