I like to start with this for new [read: untrusted] clients or small one-off projects. It can work for ongoing projects or longer-term development as well. For your customer, buying custom software/web development, SEO, network security configuration, or server admin time becomes more like buying printer ink - a simple purchase. It is easy for a secretary or project manager to "buy" a project, administrator time, or just someone to call when something comes up that might otherwise not be funded or have payment denied if fiscal officer authorization to write a check is required. If the arrangement seems to be a deal-breaker for them I can make a traditional invoice scheme work (with rates in-line for the hassle of invoicing, payment delay of 15 days or more, and the chance of not getting paid at all).

("You may request a modification of the terms I provided or inquire how to best build an arrangement to suit your specific business process. More traditional billing schemes are also available.")

I've had a few blocks of setting up office phones and network storage for a client turn into a permanent part-time IT administrator employment offer. They decided to bring my services in-house rather than paying my block rates after they saw my work ethic and how well the system I developed fit into their organization.

I don't frame blocks as a "discount" but let potential and existing customers determine on their own that the prepaid and larger blocks are a better bang for their buck.

(Linux, {Free,Open}BSD, pfSense admin, and data recovery service inquiries --> cyrus ta cyrusyunker tod com)