There are many factors affecting sales.
I can contribute a few and let's help each other to
share what affects your sales.
When you have a demo or sample, it must be working.
Check the domains if it is not expired. It happened
to me twice that my demos are not working because
I forgot to renew two domains because I forgot to
make the domain to auto-renew.
Sometimes when we create affiliate sites we link
the images or videos of the merchant but suddenly
the merchant change the image location, forgot to renew
the demo or change the links of affiliate information
or article supporting the sales letter.
Sometimes when we change the wordpress permalinks to make
seo pages the links are not found or goes to 404 page.
Sometimes when we change the on-site optimization or split testing we forgot to list what keywords are in the first page
so when we change the structure it affects the content
or when we add new keywords, the old keyword was affected.
Sometimes when we check that the keywords in our sales
letter is mis-type we edit it to correct the spelling
but we also didn't give the importance of getting traffic
on those mis-typed keywords.
Let me know your experience that affects your sales or
traffic so we can prevent it to happen again. Sometimes
simple things can drastically affect sales or conversion.