How does an investor "Buy a Contract" from a wholesaler

[Victor Boyd]

My partner and I have an opportunity to purchase a contract from a wholesaler.  He says that he has a contract and he wants 150,000 for it.  We have done the comps and think that we can repair it and sell it for about 210 to 220,000.   But, I don't really understand exactly HOW I buy his contract....   

I assume that he made an offer on the house at say, 120 to 130, and has a long closing of 45 to 60 days.  And, I understand the idea of him selling it off for a profit without really doing anything, but, I have not actually SEEN the contract.  When doing a deal like this, is it customary for an investor like my partner and I to ask to see the contract?  I certainly wouldn't give anyone $150,000 without knowing that there is a valid contract on the property for me to take over.

Please help me figuring out how this operation really works!

Thanks,