[quote=@The Omnipotent Sphere]
[@Double Capybara] Always, why?

[@Kho] Could I go Demons (Pacts)?
[/quote]

Don't think Demons is wide enough to be considered a Domain to be honest. It seems like something that would come under 'Magic' or - as Cyclone suggested - 'Evil', or 'Occult'
In fact, you could go go for Magic (Pacts) - so the pacts will be binding due to the magical nature of the agreement...and it would also mean that you could grant people some kind of 'Pact' magic which makes them create magically enforceable agreements...
Though mind you, Astarte is already a goddess of Magic