Monopoly
Trading out of debt
If placed into debt, a player must pay a debt as fully as possible on the spot. However, the player can trade to raise money to pay this debt if need be. But this trading can only take place if it raises enough money to pay the debt. If it does not, all trades are cancelled and the debtor's property is handed over (the standard bankruptcy rule). So if you have no cash and land on a £500 rent property, and another player offers to buy a property off you for £800, that deal can be accepted and the money used to pay the debt. If the offer is for £300, the deal cannot be accepted.
The rationale is that it makes sense that a player who is rich in property should not be ruined by a momentary poverty in cash. However, trading to get out of debt can be abused by a debtor. If driven to bankruptcy, they could sell all their property for a token price before it is taken off them as a "fuck-you" move. Therefore if any trading is allowed, it must be genuine.
(Not) charging rent and cooperative play
There's nothing in the rules that states that a property must collect a full amount rent when it is incurred. In fact on the spot deals can be made - the property owner can let the rent slide, accept a lesser amount or take property instead. The only limitation on any deal made is that it must be instant - a deal cannot be made that involves any future behaviour or transaction (e.g. "You can pay me next turn"). Put another way, deals can only be held to the moment. You could accept a deal that invokes future behaviour, but there's nothing enforcing such a deal. You have to take it on trust.
This leads to an interesting tactic where two or more players can form a cooperative, where they agree to not charge each other rent. In the mid- to end-game, this makes for a killer combination. The cooperative players are effectively playing against one less opponent and so in a 6 player game will be paying 20% less rent.
It's difficult to legislate against this style of play because an occasional leniency in charging rent and full cooperation are points on the same spectrum. Perhaps it is self-limiting, because other players can always form a cooperative in response. There is also a big temptation for cooperative members to defect when the chance comes for a lucrative rent.
Free parking
A common house rule is putting all taxes and fines into a pot, to be won by anyone who lands on Free parking. Schlumberger (in New Rules for Classic Games) argues heavily against this, pointing out that adds more randomness to an already random game.
Start order
Another point made by Schlumberger is that the order players start in has a great effect. On the first move, players can land on 11 different spaces. (Actually, 95% of the time it will distributed 9 different spaces, 66% of the item within just 5 spaces.) There are but 6 properties in these 11 spaces. This first player has the chance to land on any and maybe buy them. By the time the last player moves, at least some of these will have been bought. Thus they may not only miss out on a chance to buy, but they may also be fined. The bunching of possible moves only enhances this possibility. Thus, the later players are at an increasing disadvantage.
One solution would be to compensate later players with money. Another would be to auction off the starting position.
Shorter games
Play drags on for far too long, past the point where it's clear who is going to win (or who is going to lose), so an early endpoint is called for:
- Set a money limit. Whoever reaches this first, wins.
- Set a time limits, or a certain number of times around the board.
- Distribute or auction off a few properties before the game starts.