Actually, I think that saying "but I behave professionally" is equivalent to saying "I am a great lover" or "I am a very humble person" - making such a stateme

Actually, I think that saying "but I behave professionally" is equivalent to saying "I am a great lover" or "I am a very humble person" - making such a statement is an automatic disqualification for the quality you are claiming. The point I am trying to make is that if someone says "he/she is capable and behaves professionally, but the culture fit is just not there", that's when I become fairly suspicious of the circumstances.