I really believe that if you use that you may "turn off" the potential buyer...
If you must use an agreement (I have used agreements in the past and know that they are a a "must" at times)...then this is a good format to use (I've include the "cached" version in html ...easier to view)...
Not a bad start. But for $50M I think you could afford to hire a lawyer
Just a few points:
Perhaps along with all these representations you are asking the seller to make he will want you to make some representations, such as that you will pay him a certain amount of money by a certain time, etc. Not at all unreasonable
A domain doesn't infringe on a trademark, the use of it or intent to use it does.
The clause about the seller making himself available until the end of time to provide information about the name and go to court for you is absurd. I understand what you want here, but don't try to write it yourself.