Wholesaling half of a Duplex ???

[Ceasar Blackman]

Hey spoke to a seller today from Orlando and the numbers seemed good at first . He failed to mention it was part of a duplex. How can i figure the comps for this ? Its rented right now for 850 and the ball park figure he gave me for the property was 39k. I have heard of people wholesaling properties that are rented to buy and hold investors using a different formula to see if it makes sense. After i churched the number just off of the rental rate and taxes, vacancy and insurance the ROI was over 13%, i figured after my fee and improvements to the property the total investment would be 55k and thats on the high side for the area. What are some ideas about how to approach this