There are so many ways to acclimate I got really confused.
I've had better results with plop and drop but like Rachel says in the article, it and drip acclimation both work.
What didn't work was pouring shrimp in a bowl and adding a little bit of tank water at a time over the span of an hour like my first seller suggested. However, maybe if I'd added Prime and taken two or three hours I would have had more success.
I wonder if sitting in ammonia-filled water is the real culprit? I now immediately add Prime to any critter I receive.