With no allergies to hold me back, I enjoy an active lifestyle, making exercise a daily habit.

It becomes a calculus exercise. the extra thousand raises seller costs, but should cover the extra costs at the margin in most instances. 

Bob, I have gone through that exercise and came up empty.

DEFAULTS Tenant will be in default if: (A) the Tenant don’t timely pay rent or other fees and charges they owe; (B) Tenant or any guest or occupant violates this Lease, property rules, or fire, safety, health, or criminal laws, regardless of whether or where arrest or conviction occurs; (C) Tenant abandon the property; ....When Tenant is in default, the Landlord has the option to declare the entire balance (all outstanding balances including but not limited to invoices, rent, cost due to damages/abandoning the property) payable hereunder to be immediately due and payable; the Landlord may exercise any and all rights and remedies available to Landlord at law or in equity and may immediately terminate this Agreement.XVI.

Pref Rents are below "legal max" and can potentially remain there forever (or as long as that tenant exercises their legal right to renewals... allowable increases are based on the Pref rent as well.

Gently let them know that if they continue to use the HVAC in this manner and it causes the unit to fail, they will be responsible for replacing it due to negligence. 

It is fine to take a gentle approach when talking to them, but those provisions are in your lease for a reason.

Bringing the $750 Tenant to the Real WorldAs for your tenant enjoying their $750-a-month sweet deal, it's time for a gentle reality check.

It's certainly a good exercise to learn what is what in QB. 

Not sure is seller will accept an offer with these contingencies as it will cost time on the market if the contingencies are exercised.