Validation rules are used to confirm that a quote’s product combinations or quote line field values match predetermined conditions. User will see an error message if they don’t meet the condition.
The quote doesn’t get saved until the condition defines in the validation product rule matches.
In this example the window sensor is the product and you can sell only one window sensor per quote:
Product Rule Name: Prevent Duplicate window sensor
Conditions Met: All
Evaluation Event: Save
Message: You may only have one window sensor on this quote, please delete all but one
Rule: Prevent Duplicate window sensor
Tested Variable: Window sensor
Operator: greater than
Filter Type: Value
Filter Value: 1
Product: Home Console
Product Rule: Prevent Duplicate Window Sensor
If user adds more than one Window sensor it will give error