The Shoulder

Make sure that the patient has understood your question correctly: which movement mostly increases the pain ?
Repeatedly test the different resisted movements and always compare with the other side. Make sure the tests are executed in a technically correct way.
If you keep getting a variable answer, then there is a considerable chance that you are dealing with a Chronic 'Adhesive' Bursitis or with an extensive chronic subdeltoid bursitis. The latter is certainly the case if a painful arc is also present.