If the variance is insignificant, then allow it to just proceed with posting to the variance account.  If the variance is significant, then I always suggest a PO Return of Goods to take the item out of inventory, a corrected PO Receipt of Goods at correct unit cost, then the PO Receipt of Invoice.  

If the variance is insignificant, then allow it to just proceed with posting to the variance account.  If the variance is significant, then I always suggest a PO Return of Goods to take the item out of inventory, a corrected PO Receipt of Goods at correct unit cost, then the PO Receipt of Invoice.  

Returns don't work for some valuation types (FIFO / average...), and can't handle Landed Costs.  We usually do corrections with inventory adjustments and journal entries.