3 emails of valuable content always works best for me.. & this is in different niches.. Buying the product first always helps increase conversions.. What?? How?? what I do is upload 1 video or 1 chapter(if it's a pdf) from the actual course just to prove that I actually bought it.. it really makes my review more trustworthy!

But for my music production blog, emailing them 3 times a week works well for me & I only provide value, all my products & affiliate links are on my blog I don't email any offers!

What I do is create short videos interviewing salesman from different local stores reviewing a particular product then blog it & send them to amazon, it always converts well.. I know this is a bit off topic but great way to increase conversions..