@Manuel EncarnacionDon't get sticker shocked, $4,400 appears to be like a steep cost but think in the scale of the operation. 

While I don't normally offer "cash for keys" because I live in a landlord-friendly state, I felt it would be prudent in that situation because there was no security deposit and I figured if he was a little more flush with cash upon move-out, it would probably make his ability to move go more smoothly.He was too upset and "shocked" to even contact me himself and had a friend do it. 

Look really understanding and concerned and say really nicely that you can't find any evidence that there is a lingering problem but, you'd be happy to let them out of their lease with really fair terms.My experience dealing with tenants who started threatening to leave, is that when I'd actually offer them the option of leaving - they'd be kind of shocked and start back-tracking.I'd follow-up any discussion of offering to let them out of their lease in writing - email is fine. 

Several people have expressed shock/surprise when they meet me there and asked if I owned the house, at first I was honest but now sometimes I tell them my parents own it.

I'm a little shocked they can do that 12 months out.

I don't rent to wife beaters and I was shocked her sister didn't understand. 

Tenants are usually shocked by the fact that we'd do that.

Yes, I was shocked too.

Just to add to this, because this tenant likes to 'negotiate' over pointless things, I wouldn't be shocked if said tenant thinks you are responsible for washing/replacing a hypothetical landlord-provided curtain when it gets dirty through normal use...

By doing otherwise, you risk fines and/or jail time.If you find that shocking or upsetting, consult a reputable real estate attorney and ask for their input.