Can they just change the amount as they see fit? 

That would involve emotions and there is absolutely no place in business for emotions.

I have not consulted an attorney, it's a pretty simple transaction so I didn't think it would be necessary to get an attorney involved to draft an addendum.I'm curious if anyone has any experience in adding these types of contingencies to contracts that protect the buyer all the way up to the closing table?

Purchasing involves combing through perhaps hundreds of candidates over a period of months, creating a short list, visiting properties in person, bidding, hopefully winning one, then managing a rehab, and then interviewing property managers, and then hiring one.

Is this a viable opportunity or am i trying to make the pieces fit where they don't?

I had an opportunity pop up recently that involved owner financing.

You have to look for portfolio product which fit your need. 

As far as I know, when you rent an apartment, your landlord has the obligation to provide you with a living space that is fit for human habitation.

@Courtney Fricke, I don't reckon there's enough equity for a Wholesaler to get involved.

For the last 6 months, I've had short runs with different marketing techniques and have not found the right fit yet.