When I first played the game I read the entire Rules subforum on BGG to make sure I wasn't making any mistakes; these are some of the (mostly accidental) house rules I saw there:
- If you cannot do everything on a card, you cannot play it (i.e. if you do not have 2 actions in your hand, you can't play Village)
- You must use up all of your buys every turn. You must use all of your actions if you are able to.
- "+1 action" means "Play another action card right now."
- You can buy a curse during your buy phase and put it in another person's deck.
- At the beginning of your turn, either draw to 5 cards or discard down to 5.
- Break ties by counting the total treasure in decks.
- Everyone plays their actions, then everyone buys, then everyone cleans up.
- If a card gives you (say) +2 money, that money cannot be combined with any other source of money to buy things.
- If a card gives you +2 money, you take a Silver card (and so on).
- If a card gives you (say) +2 money, that gives +2 money per buy you have that turn.
- If a card says "reaction", it automatically blocks an attack in addition to whatever other powers it might have.
- After you use a reaction card once, discard it.
Some of the people declared their intention to keep playing with the wrong rules when they were pointed out, usually because they were beginners who couldn't really see how it would negatively affect the overall game. I wonder if they ever switched to normal.