PPC affiliate - One day I earn, another day I lose - Conversion Fluctuates all the time

I'm promoting about 30 landing pages for different kind of products, via PPC sources, such as Bing ads.

After a very lengthy time of optimizing my campaigns, ad text, landing pages, and keywords, my conversion rate is still fluctuating every day.

Eventually, on one given day I might be spending $100 and making $200, but the next 3 days I'm either breaking even, or even losing.

I feel like no matter what I do, there's simply no way to achieve some guaranteed conversion rate. Even if my offers are attractive, some people are just doing window shopping I suppose, and might even not stay on my page for more than 30 seconds, and some might click my affiliate links, but won't result in a conversion. There's no way for me to isolate these kind of people from clicking on my ads.

For example, on Labor Day, my ROI was about 400%, but it crashed the following days.

Therefore I suppose my conversion rate is 90% dependent on the shopper's mood, and yes, I suppose that during the holiday season it will be better - But what about the rest of the year?

How do PPC affiliates handle this scenario? I spent the last 3 years on developing all sorts of techniques, but I feel like nothing never works in the long run.

Do PPC affiliates use re-targeting for example? I never tried it because it sounds like something that will just cost more money, and is more suitable to actual website owners who can make real targeted campaigns, rather than affiliates such as myself, who can only give the same affiliate offer.