Does either require an exclusive? Why can't you use both? You can then do some tests (e.g. show both, but in random order; or show only one, randomly picked)

Does either require an exclusive? Why can't you use both? You can then do some tests (e.g. show both, but in random order; or show only one, randomly picked) to validate (or invalidate) your suspicioin that Amazon would have a higher conversion rate.