While you might not know the costs of a rehab, any contractor who is worth their weight in salt, would gladly give you a bid, if you just ask. 

I'd sign it because it would hold no weight what so ever.

As you said, mold is in the air in nature so any testing company should be able to determine whether your mold is of a dangerous kind, an elevated level, and what may be causing it.Tenants play the mold card all the time to get out of a lease or manipulate you into a rent reduction to cover their extensive medical bills.

He did pay on time, but asked for reduction in rent because the heat was too expensive. 

He then went on to list them all (an acting coach, a speech coach, a Broadway coach, etc.).Whatever you spend on a "good" coach, education program, or mentor is worth it's weight in gold.

The $10k a month I would assume is asset that guarantees it to you the income with no principle reduction and in this hypothetical scenario.  

After two price reductions I finally got it rented, but it is still rented for about 20% above comps in the market.  

We also like to give them a 2-1 reduction off the total due.

Also, it doesn't help out your brand reputation if you're constantly asking for reductions or you're hoping an uneducated buyer will come along and buy your overpriced deal.

The weight of that payment every month was crushing.