This question already has an answer here:
Player 1 has landed on Player 2's property and cannot afford the rent. Can Player 2 accept a property with money to settle the debt?
Example: Player 1 owes the rent of 500, they have 400 and a property worth 100 (according to the bank). Can Player 2 accept the money and the property to settle that debt?
This could be considered a trade and it the official rules don't explicitly restrict the time at which a trade can be completed. (However, since it could be considered a trade, Player 2 could consider the property to be worth what they want [and therefore worthless] to bankrupt the Player 1)
As a family, we have always played it so that the property is worth the equivalent of its face value. We chose this because it reflects the "real world" in a more accurate way.
However, after re-reading the rules, taking them at very face value, you should be bankrupt the moment that you cannot afford the rent after mortgaging and selling houses (if by doing that it will cover the rent).
I'm now more on the side of bankrupting without allowing for trading. However, we've been keeping high scores since 2002, it might not be worth it.
Summary: When a player cannot pay rent with money, mortgages and buildings, the rules can be interpreted in 4 ways:
- the player is bankrupt immediately.
- the player may trade with the other players, except the creditor.
- the player may trade with any other player.
the player may use the face value of the card to pay towards the debt.