The highest price ever paid at auction for an authentic Charles DuVal was $3,513 (£1,800) in 2006, which was during teh height of the art market. The image was of a young girl in 3/4 length selling oranges, which is more desirable than a less detailed bust size portrait of a woman who appears in her middle-ages. Since then, DuVal works, when offered for sale at auction rarely break $500. I do not recommend purchasing this under the pretense that it is worth $20,000 and an original by DuVal, especially given that the dates do not match. In addition the brushwork and color blending on the face and hair are sub-par.
Just checking in to see if you viewed your answer and if you are seeking further assistance?
Please let me know.
Understood, it is not unusual for private sellers to ask higher-than-market prices for objects they own as well as have misinformation on what they do own.