Leaving a mess is one thing... but I'd like to avoid him wrecking the whole apartment.

My first couple of real estate sales were nerve wrecking.  

People move everyday of the week, keep your ads up and answer calls ASAP.It's hard to show a unit not completed but if you have a firm ready date that's all one could ask for.I wouldn't list UNDER REHAB sounds like it's a wreck..

I also think he is going to use the "not fit for habitation" defense... he has no oil in his tank (I dont pay for that - lease says I dont either) although I know he has wrecked the boiler as well.

Plain and simple, Pets do to much damage and you won't know until WOOPS  and it's a wreck. just try and collect all the damages that are done once tenant has left.

Always give yourself an escape route that doesn't wreck you financially.Don't rely on the 50% "Rule" for expenses. 

Last summer my wife borrowed my truck and wrecked it.

so here is my switch i have been up and down in escrow for a month and a half and it has been a wreck using the va loan just allot i do not want to get in to.

After I run the numbers I see all that skeptism and hesitation. " I don't intent to live there so I can low ball"..The parties, maintenance etc all suggest you need someone to watch the rental before a fire, liquor, drug bust wreck one's investment. 

You will need to consider the the socio-economic aspects of your tenant base, common issues are job loss, no money today, wrecked or broken car, house guests that move in, unstable family environments, I think you get the picture.