I occasionally get requests in which the correspondent quotes a family legend - but provides no supporting information - and in most cases I cannot take such requests further.
Nearly every family has some kind of legend - and when it is investigated it turns out that it is only part true and has got modified over generations of retelling. Many families have ancestors who fought at the battle of Waterloo - in some case they did - and in other cases they were in the army at the time of the battle - but were not involved in the actual battle. In the past there were big houses with many servants - and if your ancestor worked there as a housemaid the father of her child is (according to the legend) the son of the Lord whose house it was. Maybe it was - but the house probably employed a number of randy stable boys who were quite capable ... ... And if in doubt what makes the most memorable story?
One of my ancestors is described as being involved in an incident during the English Civil War - and research shows he was only three years old at the time. However the story may be true if the child involved was his older brother.
I can only look into such legends if (1) they relate to a clearly defined individual - and (2) you have already researched back to that individual. For instance if there is an illegitimacy I need to know as much as possible about what happened to the child (marriage, children, occupation if available, etc.) and why (if you don't have a baptism) you think they were illegitimate.