This seems like a pretty neat feature, especially since I can see it allowing people more flexibility in pricing (i.e. not being locked in to the same low or high price all the time). But I'm sure it will never fire up most people like 'getting more for LESS' will.
If you don't already you might try to have the site make it a little bit more visible when this is enabled (at least as an encouraged choice on the seller's part). As is the minus in -100% isn't much and still strikes as discount. It would seem more honest as a different color (magenta vs cyan -- vaguely reminiscent of red/green, but not quite so charged with meaning) and possibly '+100%'. Buying something for more intentionally is all well and good, but at a first glance I think some people would be annoyed to find a game in a 'sale' list and then realize post-purchae that the price was actually increased.
Tangentially when it's a simple doubling ($1 -> $2) at most and the resulting price is around $8-10, I doubt most people would care, but slapping $5 more on top of $25 would be offputting when many other games are actually on sale.
P.S.
I found this article via someone using this feature for Black Friday this year.