Thank you for your reply! I found it well thought and I'll surely memorize some bullet points for my later career.
I've been very humble with my pricing so far because people don't really take me seriously if I try to pull that kind of wages. You see, I have neither a degree or the age which would do the trick. Past work is kind of there, but instead of URLs the clients I've met in person just want to know whether their software can be done. Peers my age are working in labor jobs for the normal 9to5 and some even brag how they can pull out 17 hours of work in 24 hours. I've noticed that people treat software development with the very same idea, where the young have the endurance to pull out sick work hours and where more hours equals more work done. People seem to be afraid of hiring someone who says their hourly wage is starting from 40€, especially when the person can't, thanks to their lack of experience, say how many hours they'll eventually need. Therefore, for the sake of getting any clients in my first steps of lone entrepreneur, I've decided to stick with the lump sum.
It really is a pity that I can't get around keeping the work hours as my own business, but so far I've found it easier than introducing them completely new way of working, where part of the time is spent on thinking instead of doing work. Until the latest incident, I had never even crossed the idea that the client may think they are getting screwed, thinking that the work they asked was really just that easy to do (because I was left with so little hours).
But about the price negotiation, yes, I agree with you and I'll not let them do that. Our negotiations had no agreement on the hours I should spend, so they have no reason to drive the price down because of that.
I'm going to be honest with you and tell you that I haven't made a single black-on-white agreement on what defines "done". Instead, the idea has been that I'll remain as the lone owner of the software, with the exclusive rights to re-sell it. I'm currently looking for the chance of turning the software into a SaaS, in which the original client has agreed on helping me by referring businesses from the same field to use it. So basically, I'm charging the original client one year worth of the subscription I've been planning on selling it for. By so, I'm basically securing at least one customer for the service for one year. At the same time, I'll basically launch a service which has proven to have at least some kind of demand. Plus I get free marketing from the original client on the same run.
You see, if they would be able to refer even two customers, I'd be glad, as that's the turning point where it's financially sane for me to get a LLC for my programming work (that's a huge thing for me in a country where you lose most of welfare state's benefits by starting one). Everything above that is really just a bonus. But should I get 20 recurring sales, I'd already make enough money that I could live (in theory) the rest of my life with the money I make from the product per month. You could say it's a risky shot, but as long as I can do the thing I like and get paid for it, I'll keep choosing the risk.