I would not say that there is 'an acceptable limit' of clutch judder.
Generally, a clutch should not judder in normal use.
Many years ago, a clutch was of heavier construction and also had torsion springs built into the driven plate to take up lateral movement on the clutch plate when the torque was being introduced through the clutch mechanism and the springs allowed for a smooth take-up.
Nowadays, the springs are deleted so the driven plate is solid and the torsional forces are taken up through the dual mass flywheel.
This is where the wear can take place (usually from short-shifting by a previous owner) and can lead to a judder. This will only get worse over time so I would at least insist they change the DMF and clutch at the same time before you reject the car.