This is house flipping, not arbitrage.
What's happening here is that agents involved in the sale of Alice's property provide Alice with a price of (for example) $1M, which Alice accepts under the assumption that her agent is representing her interests fairly and objectively. After Alice accepts this price, the purchase is delayed. While Alice waits to receive $1M for the sale, Eve (another agent) is assigned the property and sells the assignment to Bob for $1.25M. Bob then sells his assignment to Charlie for $1.5M. Charlie then completes the purchase, and only then is the property transferred from Alice to Charlie. Charlie pays $1.5M, but Alice receives only $1M. Eve and Bob both profit $250K each, never having taken possession of the property themselves.
[0] The tax is charged at a rate of 1% for the first $200,000 and 2% for the portion of the fair market value that is greater than $200,000. Source: http://www2.gov.bc.ca/gov/content/taxes/property-taxes/prope...
One part of that article that stands out is that this is possible because the seller is generally not getting market value, which implies that the seller's agent isn't doing a great job of representing them:
"This practice is often frowned upon in the real estate
community since it seems unethical or illegal. In practice
there is nothing illegal about wholesaling or assigning
rights to a purchase contract even if it is multiple times.
It is important to understand that the reason there is an
opportunity to wholesale is because the original seller is
selling the property for substantially less than market
value."