I am from Washington State, not DC, but I don't think there are any differences preventing you from doing what I would do...I would get some money for holding the place for them for 15 days, if they cancel and didn't have a non-refundable "HOLD" deposit, you just lost 15 days that could have been rented to someone else.

From Canada I will try to put together a kind of an apartment Bible in the book form.This will be not hot air but all mathematical ratios starting with a mortgage, income,expenses, and residue or cash flow for the month and year end.The illustration will be all real and nothing with if's like there are so many programs available on the net.At he end the reader if followig all this will derive to his/hers net worth at the year end There will be nothing missing in order how to purchase, manage and dispose of such equity.Let me know if anything like this exists.

Youre out money you can sue for in the form of damages, you could sue him for specific performance...and you could also use to prevent sale to anyone else.

This afternoon I also asked the contractor if he had any ideas and whether space heaters would be feasible, and he said each bedroom is already wired and equipped to take its own air conditioner in the summertime and can take its own electric heater in the winter and recommended electric base board heaters.

@Fred Stevenson I have a GC, heating & air, and handyman that I could have look at it.

Do a quick pre-screen before you even go meet them (prevents wasting your time too).. 

Use all electrical, plumbing, sanitary, heating, ventilating, air conditioning, and other facilities and appliances in a safe and reasonable way.D.

If there is little to no equity in a property sale ( short sale ) that has a IRS, FTB, type lien then they typically do a partial release for 0$ or for their equitable position. 

I assume similar places that can be rented in the area are about $2,500, but unfortunately, the structure oh the co-op prevent to rent the apartments.

It will also prevent them from feeling like you do give-aways.