Help Me With This Assignment Deal

I need some opinion from experienced investors. This is the L/O deal... FMV 177K-$190K The investor guy who wants to give the house (his has deed from the original seller) for $4000 assignment fee. He agree to pay the seller $168K about a year ago (at the closing in 2006) when he took over the property and occupied it with tenant/buyer in 2002 (He agree to cash out the property in 4 years. I have to sell it by Nov of2006) The tenant/buyer decided to leave the place in December since he is builing a brand new house. So...I have several months to look for a tenant/buyer. I can try to negotiate with the original seller to extend the term until 2007, but if he says "no"...I would have to put tenant/buyer with 18months option to buy. Do you think 18months is too short? The investor wants $$$ now for his new investing project (apartment). And he is selling about five of his properties. I went over the contract...and it looks very good. But...since it is going to be my first deal, I am a little worry. What if...he is just getting rid of the house because the house has a problem and etc... He seems very nice guy...but my husband is very worried and now I am... Please give me any opinion about this deal. Thank you very much in advance...