Surveying a clean pipe is the whole point: you are looking for cracks, open joints, root entry and bellies, and none of that is visible through silt or effluent.
This is why the best-value call-out for a recurring blockage is clear-and-survey together. You fix the immediate problem and find out why it happened in one visit.
If a contractor offers to survey a blocked drain without clearing it first, ask what exactly they expect to see.