According to Section H1 of the conditions of sale [pdf], EU & UK buyers at online auctions conducted by Christie’s London have the right to cancel a sale within 14 days, IF the buyer is a consumer AND if the seller is NOT a consumer. This right is not available for lots sold by consumers. If the seller of a lot is a consumer, it will be stated, and/or the lot will be marked with the symbol, ∍.
But even if that weren’t the case, nothing says property of a consumer quite like the 555th example of a 1967 Gerhard Richter offset print published in an edition of 739, and which he subsequently declared to be open and unlimited.