Meeting with the first potential seller

[Adrian Smude]

First off I'm a long time DIY landlord so I have real estate experience on that side of things.  

I've been driving for dollars and mailing out hand written yellow letters.  I received my first call last night and the talk went great I think.  It is an older couple that have a few investment properties, but this one has been empty for a year because their son moved out of it because of problems with his wife and they don't want to deal with it any more.  They own it out right with no liens, but are not interested in owner financing.  I asked about the property and she made it sound like it needs paint, cleaning inside and out but there wasn't major damage.  Today I drove by the house again to take some pictures and look at it from the side and I noticed an open window which I could see the back door was open so I'm assuming people have been inside and there's at least some water damage.  She is going to try to find time to call and meet me this weekend to show the place.  I'm most liking looking to whole sale the property, but I'm not great at estimating repair costs for something that is looking to be a big job.  Any advice on what I should do to get a better repair cost estimate?  I don't want to offer her the wrong price or offer it to a flipper with the wrong numbers.  All advice is welcome.