Deals are all about timing, whether with your financial standing or the market, or both.

That I object to and stand by. 

So if he wants "a little more than what he owes" plus the $6k tax lien you're looking at ~ $115,000 - $120,000 on a ARV or $140,000 it's going to have to be turnkey for it to stand a chance.

You have to weigh you time and effort vs the amount of money you stand to gain from him if he does end up paying.

*Another option may be to skip the door and walls and to simply put a shower stall there that has tinted glass (more tinted than the photo below but a stand alone stall):

Once they have issued a loan commitment and you have been cleared to close you have a strong legal leg to stand on.

If you are in a competitive market you will need to go non-contingent to make your offer stand out and in many cases to level the playing field.  

These are the two biggest things that stand out to me.

Talk with several professionals in any industry and a few will stand out above the others.

. - read on real estate as much as you can- Recently, I've started also going to the properties that I've evaluated to get a feel for things- check your credit and make sure it's in good standing- reach out to banks to see what they need from you to get a mortgage approval if you're planning to take that route. they will run your credit and quickly tell you if your credit has any issues. you will also get a feel of the minimum property price they will finance, the closing costs, and the down payment. the banker that i've been working with require 3% down payment if I'm living in the property, and 15% if I won't.