Pieces with this colour way have been turning up for many years. Vases, bowls(?) and lamp shades. They have been given honoray status as Aboresque Ware from S&W for as long as I can recall, but I cannot recall any precise proof of this.
They never have a Monart pontil, and by now, if they were Monart, one would have been seen with a typical pontil. Indeed, the finish of the base suggests that it has been blown into a mould. The surface has a more melted-in effect and the colours are used (together) in the way that is not seen on known pieces of Monart. Monart surface decorated wares have, on the whole, a 'dryer' look, without the sheen that appears on these items.
Therefore, I believe this is not Monart, but I can fully understand why the seller believes that it is - especially as it is the closest to a Monart shape that I've seen.
I must add my apologies to the seller, since I don't normally interfere with sales, but it's an annomally that has occured for far too long.