I am going to cover the first problems I see all the time
Claim something does not apply to get out of fixing the issue
Make up excuses to stop doing something
Try and speak down to someone else to make yourself seem more important the other client or person alike
Have no idea what’s going on such as no idea what say Linux software is or how to work.
Not able to stick to deadlines such as make app 6 months from now
Problems with other staff members so result in fights happening so one might try and break the program or damage to get back at someone they dislike which can include a client or boss alike or anyone else
Try and start arguments or fight to try and prove someone point that does not make you or the other person look better or make the system look better unless you are dealing with person scared of there own shadow if you are then to me you should not be to aggressive
Having a website keeps crashing is not good sign especially when someone just buys your software
How to make a software right ?
Understand if someone says a problem this gives you a powerful chance to make things get fixed or even better say you make a charge cost of $20 a month if you follow the other person advice so now allow to include a fancy extra feature you maybe able to put your price up to now $30 over it being a lot better designed or simply be able to perform another function
Workout what the issue is such as make a website load faster by you maybe able to convert HTML to shorter codes to decrease the load times or if you make such a cache allow the Css to put into a formula which Search Engines can process more easily allowing the speed to go from say 3 seconds to now 1 second load times.
Set realistic budget such as if something going to take your dream 1 year charging like $100 be pretty stupid since probably not cover your costs you would need to charge around $20,000 on the low depending on the full labour and costs to you so you make a profit from it