a few questions about wholesaling

[David -]

I have never been interested in wholesale therefore I don't know too much about it. I have an opportunity to whole sale a commercial office building for a nice profit so I'm doing a little research. Anyone that can answer these questions, I really appreciate it:

1. Does contract have to have a clause that says it can be reassigned or is it re assignable as long as it doesn't say it can't be reassigned?

2. The owner of this property is being foreclosed on and he is allowing me to have the property for the payoff amount of the loan. Problem is the payoff changes every day due to late fees, etc. How should the contract be worded so that the property is sold for what ever the payoff is at time of closing?

Thanks,
David