Prices are dropping because of people trying to buy lower, and people don't have patience to sell for higher. Fast sales aren't always smart sales. That is obviously someone selling only a small amount of wool. Look, I'll try selling for market price really fast to show you that it sells for 395 or higher... Watch. 1 second
EDIT: Exactly what I thought.... someone was selling only a few for like 50gp just to probably clean out their bank. Here is proof...
And just incase that isn't enough proof... I took a picture of my complete screen so you can see what time it is. JUST took the picture literally...
However, I just removed my wool from the GE because I'm selling for at least 500gp+.... It might take longer, but profits are SO much better!