I've noticed that people will put their items on sale down to a few cents. Of course nobody can buy it for a few cents because you have a minimum purchase amount - which I believe is now $1.  I'd recommend that you don't allow a single product to be put on sale for less than a dollar if nobody can actually buy it for less than a dollar.  It creates an imbalance there - people will be forced to donate the difference so it's not a real sales price and it's manipulating the system.

And also then if you put a group of items on sale it won't place any of them at below that minimum since you can't currently set individual sales prices if you select multiple items. (Other than putting them on sale one-by-one but that's tedious.)

(Also you need a search feature in the forums so that I can see if this topic was posted before, before duplicating it, but I'm not about to browse several hundred pages to check.)