Ask for each complete assembly's geometry, mass, centre of gravity and inertia, assessed against the robot's applicable limits for the intended orientations and motion, with drawing references and exclusions stated.
That is one input, not the answer; ask them to identify the exact assembly assessed rather than letting the catalogue tool represent everything attached to it.
Keep that incompleteness next to the quoted prices, so the cheaper number is not treated as an equivalent complete proposal before either supplier has supported its load claim.