I shoot a lot of pictures at various church and cultural events at the request of the organizers, although I'm every bit an amateur. I've experimented with various developers such as Sam's, Walgreen's Eckerd’s, CVS, etc., and have finally concluded that I can't use any commercial photo developer. I have never been able to get results comparable to those I get with my trusty Epson R1800 or even with my ancient Epson PictureMate PAL.
Every time I've attempted to use a commercial processor I would have 5 or 6 prints made, bring them home, and laboriously calibrate my screen. I would then edit the picture files and take the whole bunch to the store to be printed. No matter what I do, the prints still don't come back the same, not even close. I still don't know why, but they don't.
This is quite irritating, because it would be much easier to make disks and distribute the disks to 25 or 30 people rather than print them myself, but as of now that's what I'm doing. Although it costs me a bit more, I charge them a quarter per 4 x 6 print just to recoup some of my expenses.
It would be nice to know if anyone's found a commercial processor that gives good results.