It doesn't matter what you do, in my experience. It's all luck. I've sold the same condition non-key book in consecutive weeks with a $25+ difference multiple times this year. Sometimes the lower grade does much better than the higher grade that was listed a few weeks prior. Same with lower value books...take She-Hulk #60. I've sold 6 of them in the past few months.
$10.50
$15.95
$1.99
$10.01
$4.51
$6.51
That's all over the place for a low-dollar book. Nothing changed on how I list. Same big scans, same description, same low shipping charge. Sometimes the 9.2 would sell more than the 9.4, and so on. It's all luck.
It's also not just comics. Action figures, video games, etc. It's happened a LOT this year, so I don't get upset at it anymore. I just sigh and move on to the next batch of auctions.
Peace,
Chip