We're working on a kind of CMS, a fast, hosted, centralized website builder like Weebly. We also use Scrum development model. But there seems to be some problems here. Our sales manager always come to us, complaining about the design of the application, or UI elements, or stuff like that and hinder development process by making re-works again and again. Examples are:Why do you have item actions like delete and edit in grid items? Just have list actions as a toolbar on top of grids. No item action.Why red color? Use green. That's what people like.Use tree for contents, not grid.My question is really simple. Is it considered productive, or even normal for sales staff to interfere in application analysis and design? 
Should sales staff interfere in application analysis and design?
design;development process;scrum;defect
What you see as interference might simply be them trying to put over new and/or changed requirements. Your example of the colour issue is a prime example of this.However, your other examples could be seen as interference - especially the way you've phrased them.What you need to do is arrange regular meetings to discuss the direction and design of the product, but you must get them to state their requirements as either end user requirements (the user must be able to select all their widgets) or sales requirements (we must be able to show this data as pie chart) rather than as implementation details. In general it shouldn't matter how you implement something as long as it serves its purpose.There will be times when the requirement matches a specific implementation detail - e.g. showing a hierarchy as a tree.