For example, if the "original" were duped into thinking it was just going to be a transportation — Dawnstorm

Agreed. That's very much an extra portion of the set-up though. If the person isn't aware of the nature of the teletransporter, the deliberation never occurs so it kind of defeats the point.
But yes, that's potentially an issue for them. But for our discussion, it's not. They are simply misinformed.

There's a difference in bodily continuity between the person not "transported" and the person on Mars, and that difference is susceptible to ordinal description: one body is more continuous than the other — Dawnstorm

I'm not quite sure I grok, but on the assumption I do, im not sure i entirely assent to this. based on what I think is important, it is the differing mental states that matter. You could actually remove the necessity for their bodies to be empirically difference after that infintessimal period after duplication. They could remain bodily identical (qualitatively) and still be numerically different. The actually 'continuity' aspect probably doesn't need addressing in that case.

So is the person who steps into the transporter the same person that steps out of the transporter, even though the body that stepped into the transporter has been taken apart and re-assembled? — Dawnstorm

On my account, they could be considered the same person. But that isn't necessary. They could take on their own novel place in the universe, and not merely slip into the same place the P1(as it were) occupied. But, they are not 'reassembled'. They are basically 3D-printed based on the data-set beamed from Earth to Mars (in Parfit's case). So, in the duplicative case, there literally is no P1 left to be dealt with. They didn't even exist AS P1. They were P. They they were nought. Then P2. And who is P2? Is where we're getting some juice.

I think every duplication event, in light of the Star Trek version, is simply a new person who's start point was the exact same as another person at a previous point in time. They are numerically, qualitatively and temporally different people. Confusing, sure. But no issues metaphysically/ontologically imo.

Which one of you is this??
:grin:
https://www.denofgeek.com/tv/star-trek-characters-died-transporter/