So whats the big deal about the players going 1 session without magic items?
Just to point out....a CR1 spear trap costs 1200 GP to make.
So my wizard, thinking he may someday make a keep or fortress, if he wants to put one measly spear trap in, would have to, at his going rate, do 120 identifies. I think if you look at the grandscheme of the economics of a DnD world, then making a 100 some profit on a few identifies here and there isn't a backbreaker.
BTW look at rent....for a Good stay at an Inn, its 2 GP a night. So for a month its 60 GP, and thats not including meals. So make it another 30GP, for a grand total of 90 GP.
So the question then is, how many identifies does he do a month? IMHO not alot. Adventurers and finders of magic items don't wander into town every day. So for him to stay in business, continue to do research, build up a library, correspond with other sages and magickers, and so on, and still be able to make a profit to enable him to live at a lifestyle he is accustomed to, he set his value at 300 GP. The players are free to go elswhere of course.
Let's look at some real world services. An hour with a lawyer can cost from 300-500 dollars, roughly what, 30-50 GP. A doctor's visit is 250-500 dollars, again, 25-50 dollars. A mechanic charges about 65 dollars an hour for his services, so lets say 7GP an hour. I'm paying a guy a base of 50 dollars to make some decals for me, thats 5 GP for a job that, if I had the computer and printer, would take me 20 minutes to do, if that.
The wizard has spent x number of hours making identify scrolls, since he doesn't want to walk around with identify memorized, using up a spell slot he would need for defense. Saying that he is making a 150 GP profit per use of the scroll does not take into account the amount of business he gets. Lawyers and doctors charge what they do for their expertise, and usually can count on further charges down the road to make even more money. They and mechanics know they will have a steady stream of customers.
A wizard doesn't know that. At least, if you have a realistic set of world economics. Remember, in our world, a vast amount of wealth is concentrated in the hands of a few. Wizards in a DnD world would be part of that world, because they can do what others can't, and should be rewarded for the time spent learning those skills, the risks and challenges they must face.