Usually people calculate/justify the cost. Like if a new phone costs 1000 and the old phone can be sold for 750 (selling it before the new purchase or after doesn't matter) then the actual cost of the new phone will be 250.

But if we stop buying old phones from them, then they will have to bear the full cost (1000) and they won't be justifying their purchase like this.

You know what i mean right?