Lean on me

Ha... reliability... Being able to rely on someone is probably one of the best thing after peanut butter. Reliability creates trust. Trust creates confidence. Confidence creates success. The equation is simple and works both in professional and personal lives.
Reliability is not only a matter of getting the job done but, most certainly, to get the process effectively communicated. Good and not-so-good aspects of it. Meeting a deadline is being reliable. But informing that the deadline won't be met (and eventually giving the - good - reason why) also qualifies.
Now, on the requester side, how do we influence vendors, employees, co-workers, to show reliability? Constant follow-up can be a sign of distrust. Absence of follow-up can be a sign of disinterest. Where is the right balance? How do we manage the unmet deadlines and their consequences?

I am working regularly with free-lance graphic designers and programmers. I try, every time to effectively communicate the degree of emergency linked to the jobs I'm requesting. When possible, I don't impose a deadline but ask: "When do you think you can give me that by?" And then I confirm the date we agreed on. One of my deadline was Wednesday. By Friday, I still haven't received anything. Because I've found the person who's executing the job to be poorly reliable before, I had a pretty close follow-up, still trying not too be too overbearing (it was Holiday season and I respect everyone's need for time off.) I placed a new request today, reminding of the deadline we agreed on and asking for a new one so that I can, on my side, communicate effectively to my client. And I have no answer to my request. As a last resource, I started to execute the job myself, which takes time (I'm not a trained graphic designer or programmer), and probably duplicate the effort.

What is the best approach to lack of reliability? How do you deal with people you can't lean on?