In Dynamics CRM 2013 and 2015, if you use the opportunity line item (opportunity products) subgrid, when you click the + sign, you get the choice to add an existing product or a write-in product.
But sometimes you don’t want users to use write-in products. If the users must sell something from the price list, the option to use write-in products presents a potential issue, as it can allow users to create unauthorized opportunity products. That is why some CRM implementers decide to remove the standard opportunity product subgrid and add a custom opportunity product subgrid to the form, or display the Opportunity Products navigation bar item.
In CRM 2013, if you create an opportunity product from the navigation bar or a custom subgrid, the Opportunity Products form will open and the “Select Product” two-option field will default to “Existing.” This makes the product lookup available and the write-in product field disabled.
In CRM 2015, users have noticed that if you create an opportunity product from the Opportunity Product form, the “Select Product” field will now default to “Write-in,” which makes the Product lookup field disabled and enables the Write-in product field.
To change this behavior back to the way it used to work, you can use a business rule. Note the “set default’ business rule action will not apply here, as two option fields naturally have a default value. However, you can force the use of existing products with a business rule that changes “Select Product” to “Exisitng” if “Select Product” equals ‘Write-in.”
Note that this approach effectively prevents users from ever using write-in products.