You're not selling nothing, you're selling space, and taking 80% of the donation for it.

So, if I want to donate to children's surgeries, I can either donate to say St. Judes where ~82% of my donation goes to treatments and the rest supports the operations of the hospital, or buy a slot on your site so that 80% of the donation goes in your pocket.

I'll really have to spend a lot of time solving this particularly vexing quandry.

Also, HN has a rule against self promotion.