Quite often when searching for plane tickets I get only some high priced results, ridiculous schedules, etc. It makes me wonder if these are the only options to get from point A to point B or have I just missed something more reasonable and it's sold out.

Having this information could help me make a better decision on what to do next. Especially in cases when exact dates/times are not that critical for me.

I understand that most flight booking engines use the same underlying software for actual searches, but maybe there are some exceptions that could just show sold out flights along with available ones?