I'm about to finalize a $100 card trade with someone who has no references and is insisting that I send first (not that a simul-send would be any safer). Are there prior steps I can take to ensure I get reimbursed if this ends up being a scam? Thanks.

That's odd to have someone with 0 feedback insist on the other person sending first... I guess the only real way would be to have a mutually-agreeable third party do the actual trade. You both send to that person, and when the cards have shown up that person actually mails to the principals.

I would never agree to a trade larger than $10-$15 with a person with zero feedback. Regardless of the amount, I would never ship first to someone with zero feedback (unless we both had zero feedback, as with a first trade for both parties).

I would run from that trade proposition like the other person has the black plague. Either that, or insist that s/he sends first.

The rules do not insist on sending order, but this information is found in the trading guidelines for the site:

Transactions

-If there is no consensus on who sends the cards first, the person 
with the lower feedback score should (For equal feeback scores, both send
at the same time).

If you do continue with the trade, be sure to insure your package and get delivery confirmation. Require your partner to do the same.