That is a high risk strategy that works if
a) you buy the condo low enough, say 20-30% below anticipated future retail price, and such a discount is usually reserved for a few condos only or if you buy multiple units
b) you could close if you had to (i.e. have enough cash and access to a mortgage)
c) the supply and demand is in balance at the time of the intended exit (1.5 to 4 years out), i.e. there is enough demand to buy your (now more expensive) condo
As such, this is a highly speculative strategy that may work, or it may not.
It is extremely difficult to judge supply and demand 1.5 to 4 years out given the world's currency fluctuations, interest rate outlook, debt picture, local buying behavior, local condo market (both used and new) and national mortgage market.
So, the $500,000 (alleged future retail price) condo that you buy for $400,000 today may or may not be worth $400,000 in 1.5 to 4 years. Maybe only $375,000, or $350,000, or $425,000. Minus realtor costs to sell minus a few months of holding costs (condo fees, mortgage interest, property taxes).
Where I used to live in Canmore prices rose from 2000 to 2007 and many speculators, including local realtors made a quick $100,000 per condo buying pre-sales, and then in 2007 the $650,000 dropped hard to now $400,000. So, as stated it may work .. or it may not.