But it didn’t look dark on my monitor!
The great news about monitors is they keep getting brighter. But the brighter they become, the more people are disappointed by dark prints.
Dark prints are now the #1 reason prints are returned:

The problem is, the brighter the monitor, the more dark shots look normal. But while monitors get brighter each year, prints never change. They are still illuminated by the subdued light of homes, whereas photos on computer monitors get lit from behind by the ever-brighter power of flat panels.
Here’s what you can do about it:

February 9th, 2007 at 2:39 am
“Dark prints are now the #1 reason prints are returned”
I dispute that “now” bit. It has been always been a problem, since when I started working at this photo shop 15 years ago (when the only digital cameras in existence at that time were on satellites in orbit). Whenever our QC staff goes around the branches to look at the prints, the most common problem is because they were printed too dark.
The reason is simple. Each person has their own preference. A photo that is “just right” for one person may be too dark for another. Many people immediately recognize a picture that is too dark, but very few complain of pictures being too light. Photos that are slightly “too light” actually appears a bit low contrast. A little less sharp. Most people probably think it is a little bit out of focus, and not blame the photo shop.
Whenever I print photos, I usually try to print it as light as possible (without compromising the contrast too much). We get fewest complains this way.
February 18th, 2007 at 6:28 pm
[...] Guys, let’s face it: Color, color management, and skin tones are make or break for us. It’s essentially right behind “too-dark” as the number one reason why prints get rejected. Complicate matters with a wedding, where every shot is going to not only be scrutinized closely by the bride, and the families, but they want them to look perfect! We as pros have come to the realization that shooting is 2/3s of the job and what we do in post, in the “digital darkroom,” is final 1/3 of the job. You can choose to become a nut about color, about color management, and about Photoshop, Lightroom, Aperture, i2e or other software apps. Or you can let SmugMug do it for you. [...]