Wild Ups and Downs In Sales

I'm approaching 500 sales as a Star Seller and 5/4.9/5 reviews on my shop. I rely on Etsy for my income so it's really great that people have been coming to my shop -- something I know because people are constantly favoriting my items. My big question is how up and down the sales can be. For example, earlier this week, I had a day where I made almost $400, but the day after, almost nothing. I can't figure out what drives purchases besides SEO and such. My best-sellers all have many photos and video, and I'm running coupon sales all the time, so I'm not sure what else to do to make sales more consistent... preferably trending upwards. Thanks!