Jan, what you'll find is that an image optimized for a printer is not optimized for the web and vice versa. It doesn't take much to adjust between the two so they have similar appearance;
Oh, yes, I know, but I hadn't even considered tweaking my workflow towards printing from the very start of it.
I usually do tweaking for web or printing as the last thing.
usually some tweaking of contrast bridges the gap between them, as well as saving web images in sRGB rather than RGB colour space.
I've made a nice pair of keyboard shortcuts for the most-used commands in that regard; "Edit"->"Convert to profile" and "Image"->"Mode"->"8 bits/channel". An action could probably be justified, since function keys can be assigned to running these directly.
Adobe has a "Save for Web" command which helps alot to get the images just right for web-viewing conditions.
The "Save for Web" feature is kindof nice, but I've stepped away from it for my own web images, because I want to share most of the EXIF information. "Save for web" strips all the interesting bits.
Although I am not in this business myself, it is obvious that any photographer trying to sell images over the internet must know how to manage these adjustments so that the web view will look very similar to the finished print, and it is feasible.
It is feasible if your customer-to-be is using a calibrated monitor of sufficient quality. Otherwise, almost all bets are off. I've gotten the strangest complaints about how some of my sRGB converted images look on uncalibrated monitors, even though they look fine on the six or seven different monitors I can check them on myself.