[Translated into English by me from German translation by Ferdinand Leiter, Vienna, 1929.]
 Vatsyayana

Kamasutra
 

2.9
There are two kinds of impotents, masculine-looking and feminine-looking. The feminine kind imitate women in all things, in their clothing, way of talking, movements, delicate attitude, reserve and shyness, gentleness and modesty. The actions that normally take place in the groin of the woman are completed in the mouths of these members of the third sex. This is called Auparishtakam ["superior coitus" or oral sex]. Impotents get particular pleasure from oral sex, as well as their livelihood. They lead the life of courtesans, especially the feminine kind.
The masculine-looking impotents keep their practices secret. If they exercise a profession, it is usually that of a masseur. Under the pretext of a massage, such an impotent grabs the thighs of his client, then he touches his buttocks and the groin or the lower back. If the penis becomes erect, then he rubs it with his hands in order to keep it in this state. If the man then, recognizing the intention of the impotent, does not command him to continue, then the impotent does so on his own. But if he demands it, then the impotent refuses to grant his request, and only reluctantly lets himself be persuaded after much pleading...

6.1
Men with whom a courtesan should have sex only for pay [i.e. not for love], are the following:
Men who are independently wealthy from having a pension.
Young people.
Men who are not tied down anywhere.
Officials of the king.
Men who earn money easily.
Men who have secure sources of income.
Men who think themselves very beautiful.
Men who like to praise themselves or hear themselves praised.
An impotent who wants to be taken for a full male.
A man who despises his caste peers.
A man who is generous by nature.
A man who has influence on the king, his ministers, and officials.
A man who is always happy.
A man who is proud of his money and assets.
A man who does not obey the laws of his ancestors.
A man who is too grown to listen to his parents.
A man who plays a great role in his caste.
The only son of a rich father.
An ascetic who is tortured inwardly by his desires.
A hero.
A physician to the king.
Old acquaintances.