There is clear support for the presale estimate in auction records (e.g. Askart.com for 3 of the 4 Spong watercolors listed therein):

Title/Subject: A Christian Procession in the Travessa de Palma, Lisbon, signed. Watercolor on paper. 11.73 in. x 8,74 in. Sold for $2,978 on 4/23/2008 at Christie’s, London.

Photographic Image Not Available

Title/Subject: Mosque of Rab El Zameleh, Cairo, signed. Watercolor on paper. 25.20 in. x 17.32 in. Sold for $3,928 on 12/04/1994 at Sotheby’s, Sydney, Australia.

Photographic Image Not Available

Title/Subject: Hampden Avenue, Darling Point, signed. Watercolor on paper. 9.45 in. x 13.39 in. Sold for $1,484 on 09/14/1987 at Geoff Gray Auctions, Rosebery, New South Wales, Australia.

See Artprice.com for these key examples of Spong’s work:

Title/Subject: Cairo Street Scene, signed. Watercolor on paper. 18 in. x 26 in. Sold for $1,501 on 10/23/2006 at Christie’s, London.

Title/Subject: Mosque Of Rab El Zameleh, Cairo, signed. Watercolor on paper. 25 3/8 in. x 17 1/3 in. Sold for $3,950 on 12/05/1994 at Sotheby’s, Sydney, New South Wales, Australia.

Photographic Image Not Available

Title/Subject: Hampden Avenue, Darling Point, signed. Watercolor on paper. 9.45 in. x 13.39 in. Sold for $1,484 on 09/14/1987 at Geoff Gray Auctions, Rosebery, New South Wales, Australia.

See Artprice.com for these key examples of Spong’s work:

Title/Subject: Cairo Street Scene, signed. Watercolor on paper. 18 in. x 26 in. Sold for $1,501 on 10/23/2006 at Christie’s, London.

Title/Subject: Mosque Of Rab El Zameleh, Cairo, signed. Watercolor on paper. 25 3/8 in. x 17 1/3 in. Sold for $3,950 on 12/05/1994 at Sotheby’s, Sydney, New South Wales, Australia.