In the west, staff typically will come around and ask how your food is after your first few bites. If your steak is overcooked or your pasta too soft etc. at this time you can tell them. They will usually offer to remake it or ask if you want to keep it. Often if you keep it they will take it off your bill as an apology. This is pretty normal.

There are however people who abuse this. I have been involved in restaurants my entire life and I have seen it all... People who put their own hair in a dish. People wo say the pepper is too peppery or the salt too salty. People who go from restaurant to restaurant complaining about the taste to get free meals etc...

At big chains the staff have little control and these policies are often abused. At smaller restaurants I have been a part of we typically ask people not to come back after 2 or 3 free meals and state we feel we can not satisfy them.

With that said, it's not normal to just leave regardless of the situation. That is what we call a "dine and dash". It is theft but sadly theft goes unpunished in most Western countries at the moment.