or would u generally interpret that lease language as meaning late fee applies starting 4th itself (which is what I have communicated to him in the past)?  

Always make sure your contracts are assignable for tax purposes (we use a form paragraph added to the contract, consult a lawyer for appropriate language), build in a study period and have contingencies laid out for release of documents and financial records of the property. 

He added that language because we are not interested in doing additional work.

Plus, I had the 203k consultant do a feasibility study this week which was $500 cash out of pocket.

I own the duplex and have language in the lease that the water/sewer charges will be split between the two units.

Based on this study: http://www.naahq.org/sites/default/files/naa-docum...

You can cause a seller a financial loss, this is a "Tort" look that up and study what "tortious conduct" is.This is just part of the unethical side of wholesaling when offers are made by those who don't have the ability or intent to buy as agreed and disguising their true intent. 

You should start with a entire in-depth study of both real estate investing and finances.

So I kicked the habit - I stopped going to seminars and started to apply some of those ideas that were preached by speakers who were experts at extracting fees from me.I started to attend real estate auctions, studying the process - watching others make a lot of money - I decided to get a credit line - increase my credit card limits and started looking for properties (cheap- ugly buildings) in the neighborhood where real estate auctions were taking place - my primary goal at this time was to learn the market in the area where I wanted to control real estate - I would look at 50-60 houses (but made no offers - when agents would try to qualify me I just said "I have a small inheritance and will not need financing) - I kept a journal of the price per square foot,  comparing properties, and all comments made by sellers and agents (this helped me to find the seller dominate selling motive),  that was helpful - but I soon discovered that I was just looking for real estate in the conventional way  - I needed to do something else - so I started to look for owners of real estate who had problems (I applied Power Prospecting formulas) and at the same time studying creative real estate techniques from the old masters in the industry - became a member of the Washington Real Estate Exchange, hosted a real estate investor club and started to give mini creative financing seminars  while networking with those I wanted to emulate. 

My recommendation  is to read and study and get to know your market - This site and the meetup groups are so helpful.