I want to see if anyone here can substantiate this.
I used the $10 off $35 coupons twice, same credit card #, different emails (myemail+jet@gmail.com, myemail+jet2@gmail.com) and they caught it. Price reflected $10 off when I placed order but posted on my credit card (no longer pending) as the full amount.
I complained multiple times and they refused to refund the $10. Accused me of trying to game the system and say they track coupons via CC number.
YMMV...