how to customize the sales report by item by preferred vender

I don't think there is any way to include the preferred vendor on reports that include transactions (as compared to list reports like the vendor contact list.) 

I think this a big weakness in quickbooks. Because this is ABC of the reporting system. Evry sales manager or sales owner would like to see how the products from specific vendor doing in their business.

and you know what? The purchase per item also not able to customize the items according to vendor 

I appreciate the prompt reply, Salwan.

In QuickBooks Desktop (QBDT), sales reports don't include vendors but customers instead. You might consider running the Transaction List by Vendor. This shows all the transactions associated with the vendors and you can customize it base on your preference.

Here's how to get there:

1. Go to Reports.
2. Choose Vendors & Payables.
3. Click Transaction List by Vendor.

Also, regarding the customization option for purchase per item, you can do it by running the Purchases by Item Summary or Purchases by Item Detail. Then, customize the filter to show items per vendor.

Here's how:

1. Go to Reports.
2. Choose Purchases. Then, Purchases by Item Summary or Purchases by Item Detail.
   
3. Click the Customize Report button.
4. Choose the Filters tab.
5. Search Vendor Type from the Filter List and select your preferred vendor.
6. Click OK.
   

Find out more about managing reports in QuickBooks Desktop through the following articles:

• Understand reports.
• Customize reports in QuickBooks Desktop.

Feel free to drop a comment below if you have any other questions about customizing reports. I'm always here to help. Have a good day.

They asked for a SALES report not a PURCHASES report.