A player lands into someone´s property and they are supposed to pay $1000, they don't have enough cash (only have $600) but have property and houses they can mortgage. Can the two players agree to say I owe you $400, will pay later when I get the money?
You must do everything in your power as the debtor to pay off the debt
- Count your cash
- Sell houses
- Mortgage properties
If you then still don't have enough you can ask other players to buy the mortgaged properties from you to raise enough cash. This could come from the person you owe money to. Otherwise, you are declared bankrupt.
In practical terms, not many players want to continue playing with no money and wholly mortgaged properties, therefore usually bankruptcy is the best option.
Yes and no. The rules state that if a player cannot pay what they owe, then they are bankrupt and out of the game.
However, any trades are allowed, so there is nothing stopping players from trading $5 for $1000 so that they have enough to pay, and promising to trade back on a later turn. But if they do this, there’s no way to enforce that future trade. The player could simply go back on his word and he would not be breaking any rules.
Anything in Monopoly has value if another player ascribes value to it, and this can include non-tangible things. The only specific rule around loans (based on tournament rules) is that "Money can only be loaned to a player by the Bank and then only by mortgaging property" (page 10, Miscellaneous). That would seem to preclude "I will pay you back" and "IOUs" (except when the bank runs out of money). Whether that includes "Gifts" is another question entirely.
However, certain versions of Monopoly have introduced alternative "interests" that can be traded, which inherently gives them value (the value of which is determined by the other players, of course). On the Playstation 1 version of the game, for example, a player may offer instances of "Rent Immunity," whereby the owner of a property chooses not to collect rent the first X times the receiver lands on a certain property.
It's unclear whether that is officially allowed by tournament Monopoly rules ("loan" is not defined very well), but it demonstrates that there are more ways to resolve a debt than via Mortgages and Bankruptcy. It is presumably also at a player's discretion to accept less than the required amount of Rent. Likewise, a player could simply "forget to ask for rent." The tournament rules do specifically call out this scenario.
The owner may not collect his/her rent if he/she fails to ask for it before the second player following throws the dice. (page 8, Paying Rent)
In your case, if you did not want to eliminate the payer, you could simply "forget to ask" and have the next player take their turn, and the debt would be nullified.