Miles selling websites - where do they get their miles?
 

e.g. The Mileage Club etc - offering pretty steep discounts on miles purchased.

Reading horror stories on here I don't want to get involved, but I'm still intrigued about how they work, given that apparently the airlines don't approve of them and view usage of them as strictly outside of their T&Cs.

Where do they get their miles then?

Apologies if this is in the wrong forum.