I don't think it's painful. But you do understand, your soul also includes your free will, at least for a short period of time. Or is that not part of the deal? The intention is to get your soul, turn you into a god or a goddess, and perform a public ritual in front of many people. This is usually a private ceremony, with only members of the group present. The notion of hieros gamos does not presuppose actual performance in ritual, but is also used in purely symbolic or mythological context, notably in alchemy and hence in Jungian psychology.
Johnny Blaze sold his soul, but he got super biker powers. You're just going to get money, a virtual one at that (albeit, decentralized and not connected to any government.)