Diana,
using a lab for prints and fulfillment has one additional advantage: someone to blame . From every show I shoot, I'll get one or two people who, in an effort to get an additional print for free, will tell me the print they received from the lab wasn't any good: color was off, too light, too dark, etc. So I tell them to send me the print and I'll make sure the lab corrects the problem and sends them a reprint right away. Curiously, I never get the print from those folks and the "problem" miraculously goes away.

BTW, I seed myself on every 3rd order and receive a print to check print quality so I have a pretty good idea what the clients are receiving.

Jim