As someone who occasionally prints for others, I'd very much agree with those who say that it is your skill and expertise that you are selling, not just the fact that you have a big printer in the room next door to your office.
If people choose you just on price, then you are getting customers that are not so interested in the skills and experience you bring to the print. Much as with my commercial photography, if a potential client asks the price too many times at the start, I'm inclined to take it as a warning.
Printmaking is a service that I don't currently advertise on our web site, since first and foremost I'm a commercial photographer, not a printer. Where I do print work, I like to physically see and get to know the people wanting prints, both to discuss what it is that they want, and that tricky issue, of whether their image is up to the quality required for a big print - something less likely IMHO with someone primarily worried about the price ;-)
However... my wife Karen has just started working for the company as Marketing Director, and I think she's looking at the big printer and wondering why it's not making a bigger contribution to the bottom line ;-) My own large prints are very much a personal thing, so sometimes you do need someone with a bit more of a business eye, and not involved with your 'art'.