The following was provided by Peachworks Support, using Empire invoices as an example of an invoice that when imported to Peachworks, does not map correctly.
The main issue with Empire invoices is their lack of a clear case size description, making them difficult to import. To determine the case size, one must divide the unit price by the bottle price. Additionally, when items are imported as pending, the unit is listed as a case, but the pack size is incorrectly picked up from the "Size" column, which reflects a single bottle instead of the entire case.
When the items come in with an incorrect pack size, they can be corrected when linking them to an existing item or creating a new item by adding a new Unit Description:
After saving the new Unit Description, you'll see that the Pack Size is still incorrect, so you'll want to go into the item and update the Unit of Measure and vendor product Pack Size to reflect correctly. 
The Rancho Alegre Blanco did import incorrectly because it's showing the Unit as Each instead of Case on the invoice. Still, because the item number is the same, it falls under the pending item Stillwater Existent from a previous invoice imported with the incorrect name.
You can still use this pending item to link it to the existing Rancho Alegre Blanco item by following all the same steps above, but also updating the Vendor Item Description on the item.