William Bateman Platter $?

Hope someone can help me with this item. My friend wants to sell it, it was his Grandmothers. Does anyone have an idea of it’s worth?
The piece was made by William Bateman I, in Geo. IV 1829.
The weight of the piece is 28.93 troy ounces
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Thanks in advance!

The date is correct, however, I would say the maker’s mark is for William Brown who first entered his mark in 1823. William Bateman II had his mark in a more elliptical square. Brown had his in two overlapping circles with a pellet between the letters.
A heavy platter like this would realise in the region of £600 or more in auction. Others here may disagree.