It is an old building, so sound between floors carries easily.

It is because I  have generally found that there are enough petty, vindictive, and ignorant realtors out there, that they could easily file unfounded grievances against me or otherwise make my life miserable.  

That's an excellent -- and very important -- question...Here are the reasons I have/would mentor someone who could easily turn into my competition:1.  

A lot of routine fixes can be pretty easily done yourself.

It includes many anecdotal stories, makes some great points and can easily be used as a reference for years to come. 

In this range the rental returns are easily 10-12% all cash, and you have a great working class tenant profile.I personally have one rental that is worth over $250k and while the tenants have been awesome, the turnover has been high.So at the end of the day, just try and pick a goal first, and then choose a strategy from there.

Further during a period where supply outstrips demand being the unit that gets further down VRBO's funnel of filters and having more amenities will get you the bookings the others do not. 

As he's a realtor, should I abandon the plan, as if he wanted to sell he easily could in theory?

So even if you are conservative about your costs, that one deal easily grosses 100K.

First, the MLS Mobile App here automatically pulls up properties in a consumer's current location, if no filters entered, it shows the most recent Sold flag on top of the Active flag.