Need help evaluating as deal !!

[Benjamin Chadwick]

in 2013 i bought a duplex from a guy who had over 200 units.  I lived in one side and fixed them up as he was renting to section 8 tenants and the place was run down.  the area has since gentrified and i bought in the 150's and it now appraised at 260K its a cash flow monster with both sides rented out im getting $2600 a month in revenue and total profit after everything is $1253 a month.  

I want to get another property im looking for a four plex or a triplex, so i called the guy i bought the double from and asked if he wanted to get rid of anymore of his properties in his portfolio.  He said yea, he said he would give me some properties at 90% of market value and if i was interested would set me up with a lender he works with.  I am still new enough i dont know how to really analyze a deal.  Is 90% market value a good deal?  Does anyone have a good spread sheet or tips to help me analyze the deal he sends over?