Haven’t done it yet–just reading and planning. From the install guide (emphasis mine):
Windows / Mac OS / Linux
From the Etcher application interface, select your .img file as “the image”
From the Etcher application interface, select your USB flash drive as "the drive"
Click on “Flash!”
> Next to the drop-down is a icon you can click on to enter the location of your factoryreset.img file.
It sounds as if you’re selecting the .img file twice, the first time before the drive containing the image is selected, which doesn’t seem to make sense. Is this correct?