If you can keep tabs on other people, I like to get hotels, watch someone scramble to match me (trading at a loss to get a set, mortgaging everything else, etc) so they don't hemorrhage money to me, then downgrading to houses just before they cross me.

Only actually pulled this off a few times, but the pain in their voice as they were forced to sell their hotel, just barely, to pay rent, but had to downgrade straight to nothing, and they know I have all the houses now, that's even sweeter than just getting the houses in the first place.

Once someone teased me a property giving me a second set, so they'd have a first, only for me to do this to them after getting lucky and getting the browns to hoard houses on. Quick game, no one was happy.

Sidenote: winner picks up is a role in my household. Gives the losers a way to go "ha ha" and helps keeps bad feelings at the game table and not afterwards.

This is the real way to destroy families. I've never felt dirtier playing a board game.