I believe there is a law that prevents  real estate pre approval checks from negatively affecting your score.

Hang onto it as an additional deposit.Because when she goes that sink is probably going to go with her and the repair will be whatever gets the job done the cheapest, code or not.If she's not advertising a professional salon and just doing a few friends hair for cash side money, she will do that in the kitchen if you make her take the sink out of the basement (meaning its hard to prevent it)--so I'd probably ignore it--as long as its not a real business.I'd also have the plumber look at the installation when he's putting in the Hot Water Heater and make sure no plumbing issues are present such as water taps below drain water level, etc....Good Luck!

Nevertheless, that does not change the answers.A landlord may enter the unit with 24 hours notice, and you are not allowed to prevent entry.

As a landlord I would pay the $300 and then ream the contractor to reimburse me for the cost.... no way is the tenant on the hook for this.Now if this was due to some issue that was totally out of my control or not preventable..... the pipe just spontaneously broke etc, then it would be on the tenant... that's why they need renter insurance.

There are ways to prevent them from selling to another buyer should they put the house on the market again in Feb.

What's preventing the seller and end buyer "hooking up" and meeting after the expiration date and cutting out the "wholesaler" me.

Thanks to anyone who takes the time to respond, this one has been (stupidly) causing me a mental roadblock and preventing me from taking action steps.

Your perspective might have just prevented me from making an expensive mistake. 

Perhaps a short purchase/sale contract would get things going and the contingencies will give me an exit if legalities will prevent it from closing? 

Yes, they can cost you 10% of the rent income but a good one will actually put more money in your pocket by protecting your asset, keeping you at market rate, preventing losses due to bad tenants, etc.