What is 'be beaten up an extra 2½ per cent on a provisional agreement'?
He went to see Ross and laid before him the plans for Canoes on the Rushmere. Ross professed himself delighted and allowed himself to be beaten up an extra 2½ per cent on a provisional agreement. But of course nothing could be settled, he pointed out, until he had consulted Cromarty.
(Chapter 5 To Love and Be Wise, http://gutenberg.net.au/ebooks08/0800551h.html#ch05)

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Answer

Here, "provisional" means not final, since he has to get approval from his partner. "Beaten up" means that he agreed to give up two and a half percent on the price.