While the idea of the discounts is nice, getting high tier upgrades and equipment for practically free at the whim of chance is not something that feels particularly rewarding, if money wasn't so abundant because of this it would even make me hesitate to really purchase anything knowing that the next day it could just drop to 10% of its original price.
Maybe some more structured system where lower tier upgrades could go on sale at set points to help you catch up or round out your character better later on?
Even just a more strict limit to how severely something can get discounted, 25% max.
How the system feels to me aside, at the present its also extremely exploitable.
Say crossbow bolts go on sale for 50%, price is down to 7 gold, I can sell those to the fence for 7 gold as well, so now I can infinitely buy and sell crossbow bolts until my shop level is immediately maxed out on the second day.
Not really something that should be able to happen, would think it would be pretty easy to catch in testing, but it seems the devs might have been at a point where they just had to get this game out the door, understandable to a degree.