I am about to make an offer on a vacant 2/2 two story duplex (each story 1/1) worth around ARV 210k.
The owner estimates 40k on rehab. He is asking 135k. Owner financing is available.
The owner purchased it for 22k in 8/06 and put about 6k on rehab!
I will be assigning it to an unknown investor.
What should I do, make an offer? How much? How and what should I say that would help him accept a lower offer?
How will I fill out the contract if I don't know if the seller will be receiving all cash or owner financed? How much assignment fee should I ask for?
Thanks so much!

I don't know about your area, but here a 28K (22 + 6 on rebah) house or even a 210K two family house is a gift. They basically don't exist under 350K and that's for a house in bad shape.

So you're saying the house is worth 210K and the owner is asking 135K + 40K = 175K. You basically have 35K to work with if all the numbers are right. I'd suggest lowballing him real hard to see what he's willing to let it go at. If you say he's spent 28K total, try to double what he spent make it 56K. See if he comes back with a counter offer. That's a great return on a six month investment.

I'd make a lowball offer. If you think you can make the 35K from the retail value, go for it, but if it's like here prices dropping like crazy don't even bother since 35K might be what it's really worth now. The easiest way to accept a lower offer is an all cash deal, or a mortgage commitment.

You fill out the contract in the owner's name and don't worry about the rest.

Your assignment fee should be a mix of how much you spent, how much the investor is willing to pay and how much you think your time is worth. Only you can really answer that question.