If your reason for vegetarianism is mainly prevention of animal suffering, shouldn't you be concentrating on ethical farming? Or are you against raising a happy cow and painlessly killing it some time later?

In principle, it might be better to support companies making ethical meat than to entirely boycott meat. In practice, companies lie about their practices all the time, and things that are marketed as something often turn out to be something else entirely. At least for me personally, becoming certain enough about the ethicalness of a meat product that I'd feel confident about buying it would require far more time and energy than just achieving the certainty by avoiding meat overall.