How product-led companies sell in the product experience or non-annoying UX/UI

In research mode in terms of upselling POV.

Looking for good examples of how other companies sell in the product experience - i.e in upsell/Converting free users to paying customers. Basically examples of how they sell in effective ways. I suppose people usually look at Dropbox, Spotify, Basecamp, Headspace etc. Also wondering any other products I should check out?