It's not that these people don't know, most of em don't care. They see the bottom line and the bitch fest commences.
I'm guilty of undercharging if anything. A personal good friend (I was basically on a near best friend basis with his son while I grew up) has a mailing business. They buy and print postage. So "junk mail" basically. They get sent the junkmail, the buy the postage through a software, and print it on the things they are mailing and then drop at the post office.
They have this 25 ish year old printers that do the job. Bryce / Secap type units.
Over the years I've done a lot of work for him including upgrading his computer systems twice, OS updates.... repairs, upgrades and managing these legacy printers on modern OS's hasn't be trivial.
Anways, I get a call from him the other day. His printers won't print. Ended up getting a replacement printer, but it's the exact same as his old printer. I spend a good 30 min via teamviewer trying to save myself the nearly one hour drive to get over there. I eventually end up figuring out the issue.... the virtual printer port mappings weren't correct (he changed physical USB ports). Bingo. Printing away.
He was rather anxious about the whole thing as he had a few critical jobs to get out and couldn't afford for them to be late.
As we end the call, he asks me what he owes me. To tell you the truth, I wasn't set on charging him at all. I mutter "How's $40 sound". He instantly shot back "I'll send you $100".
Our knowledge is worth something folks. Most people balk. But I'll tell you this... last summer when the HVAC tech came out to replace a simple $55 part on my central air unit... they had zero qualms about charging me $240 for the trip and the labor. That's even after the part was covered under manufacture warranty. I'm sure I'd have paid over $100 for the part if it weren't. The HVAC folks, the bank's mortgage interest, the mechanic at the auto repair shop.... they don't hesitate to charge us. So you when it's your turn you have to charge too.