Another way to look at it is the time spent already is a sunk cost.
Figure out how much time it will take you to finish, and your effective hourly rate to get the remaining $10k. If it's a reasonable hourly rate, go ahead and finish. Otherwise, walk away.
Also, that's why it's better to work hourly rather than fixed-price. That way you avoid arguments when the client increases the scope.
You don't need to always have an airtight contract. What I do is make a limit on how much I'm willing to risk, and once that limit is reached I stop working until I get paid.
Comments
Another way to look at it is the time spent already is a sunk cost.
Figure out how much time it will take you to finish, and your effective hourly rate to get the remaining $10k. If it's a reasonable hourly rate, go ahead and finish. Otherwise, walk away.
Also, that's why it's better to work hourly rather than fixed-price. That way you avoid arguments when the client increases the scope.
You don't need to always have an airtight contract. What I do is make a limit on how much I'm willing to risk, and once that limit is reached I stop working until I get paid.