Not behing payed after software is complete...
Whanted to go freelance when I was 20, got a 'real job ' and stopped programming for years...

Yeah, it really takes it out of you at times 😫

Always include a little backdoor. I like to do that and, if paid, submit a "patch" afterwards.

Well.. This was when windows 98 was out...
No matter, the software was to merge phone book databases (the costumer stole a phone book listing in paper and hired people to pass it on to an access database...
I knew what the client would have problems with (merging the databases and check for duplicates)... Two weeks after he told me he didn't need it anymore he called me to solve this problem..
Just told him I got mad, deleted the code and software and was working somewhere else...
He just had to hire a software firm and pay at lest 10 times more...
I didn't really delete the program, gave it to an uncle to use as phone book for clients