Cosmic Castaway

You aren't human, Bell. And you're not a robot. What are you? Bell pondered the query slowly, cautiously, with his semi-mechanical superbrain ... a brain that Plutonians dubbed the most deadly and dangerous in the universe.
Atmosphere in the ticket agent's office seemed thicker and warmer than usual, but the disturbing factors were supercharged emotions, not jammed pressure-gauges or thermal adjusters. Not all the emotions were human; but they were real enough, both to Bell and to the ticket agent.
I know all about you, Bell, the agent said, looking over the half-man curiously, with a hint of vicious resentment. Like many minor functionaries, the ticket agent took the troubles of his employers personally, and Mines, Inc. on Pluto was a subsidiary of the Power and Transport Trust. Sure, you think you have return passage coming to you. Hasn't the company been more than generous? Actually, it must have cost a fortune to patch you up.
Like many minor functionaries the ticket agent studied the half-man with a hint of vicious resentment.
It did, Bell admitted. But that's not the problem. I'm not claiming free passage. I have money to pay.
Bell was half-man, half-robot, the result of one of those hideous accidents never mentioned in the Company's much-vaunted Public Reports. Technologically, even aesthetically, he was a work of art, but his own mother would not have known him. Item by item, his appearance was curiously humanoid, but no elasticity of definition could make him human. Every vital organ was partly or wholly artificial, 64% of his body being either reclaimed or synthetic tissue. The face was a mask of stainless steel, washed to flesh color by aluminum bronze tinted toward copper, and the brain behind it was not the one he was born with.
Closing his ledger with a bang the agent snorted. So what? I don't care if you own half of Pluto. You're still out of luck for passage home. We're booked solid ... six months ahead.
You're a liar, Bell stated flatly, and even if you were a good one, I know better. There've been four cancellations by miners who couldn't pass physical for space. What's the gag?