Even if you have leverage, the client needs to be aware of it in order for it to work.
The problem is, the way services are sold and differentiated makes as much sense as a world where people lumped medicine and candy together in the same category. The clients repeatedly try to use tactics that makes sense for the routine, commoditised services because they served them well in the past.
But while you can get a meaningful result out of comparing price per gram of lollipops and pralines, doing the same type of measurements to compare price per gram of laxatives with anti-depressants would give you nothing of value, especially if you only need one of them.
In order for this warped comparison to stop, you need to be able to clearly show that it makes no sense to try and beat you down on candy if what the client needs are medicines.
And that’s something I routinely do.