This is equivalent to betting on the margin — the downside is that you end up holding a contract that commits you to paying for the whole condo, and if you can'

This is equivalent to betting on the margin — the downside is that you end up holding a contract that commits you to paying for the whole condo, and if you can't get rid of that contract when the market goes down or you become incapable of paying, the developer will sue you (see above comment about what happened in 2008 in Vancouver).