Im not completely sure but it could be a Polish Lowland sheepdog or a petit basset griffon vendeen (french basset) most likely the first i hope that helps
I own and breed Polish Lowland Sheepdogs but haven't seen the Advert. Do you have a link to it as could tell you if it is a Pon or not. Have to say that I don't think Pons are at all similar in appearance to Petite Basset Griffon Vendeens. Can send some photos of pons though if it will help.
Take care,
Chris.