I've recently been in contact with a SaaS company that failed in part because they changed their revenue model from pre-pay for something somewhat easy to deliv

I've recently been in contact with a SaaS company that failed in part because they changed their revenue model from pre-pay for something somewhat easy to deliver to something quite hard to deliver. Along the lines of 'pay (by buying 'credits') for any response to your marketing' to 'pay (by buying 'credits') for only positive responses to your marketing'. A deal isn't closed until both parties have done their part, and, as you aptly describe, until one has done the delivery any payment is akin to a debt, and hence it's a liability or risk until the customer got what they signed up for.