You buy a vacant lot, build a home on it, move into the home for a few weeks and then you sell the home for a tidy profit very soon thereafter. You claim the principal residence exemption (the PRE) so that you don’t pay any tax on the profit, or so you think. The CRA, of course, has other ideas. It reassesses you on the basis that you engaged in an “adventure in the nature of trade”. That is, the CRA takes the position that you were carrying on business, of a sort, and so it treats the profit as ordinary business income. The full amount of the profit is included in your income, rather than one-half, and the PRE applies only to capital gains, not business income. The CRA also assesses GST as if the taxpayers were home builders. See Sangha v R, 2013 TCC 69, which applied the factors set out in Happy Valley Farms Ltd. v R,  2 C.T.C. 259, 7 F.T.R. 3, 86 D.T.C. 6421 (FCTD), to determine whether the appellants engaged in an adventure in the nature of trade.
Neil Armstrong notes that the CRA believes that WIP under contingent fee arrangements is not income for the purposes of the Income Tax Act until the client receives amounts under a settlement or court order (when the liability of the client for fees is actually triggered).
Mr Armstrong writes:
There can be arrangements under which the fees of professionals respecting an acquisition or sale, financing, or reorganization contingent on lenders’ or shareholders’ approval, cannot be rendered until the closing, with an indeterminate “haircut” to be negotiated for a failed transaction. These may be contingent-fee arrangements.
Neal Armstrong reports that the Quebec Court of Appeal, in Emballages Starflex Inc. v Agence du revenu du Québec, 2016 QCCA 1856, has held that a corporation cannot deduct a gift to a charity as a business or promotional expense. The Court of Appeal cited Symes v Canada,  4 SCR 695, 1993 CanLII 55, as authority for the proposition that an amount should not be deductible under general principles as a business expense “in the face of a specific and complete regime” (here, presumably, for the deduction of charitable gifts).
From Philip Friedlan and Adam Friedlan, “When Does the Operation of a Rental Property Become a Business?” Tax for the Owner-Manager 16:2 (April 2016):
[McInnes v R, 2014 TCC 247], which was decided under the informal procedure rules and has no precedential value, does not break new ground. Nevertheless, it provides a good review of the law on the issue and serves as a helpful reminder of the factors that influence when income from a rental property ceases to be regarded as rent and is instead viewed as income from services.