So I've always wanted to own the house next to our primary residence...

I've reached out to the current owner about 3 times in the last year and 1/2.  He's told me twice that he wasn't interested in selling and the 3rd time ignored me entirely. (I had sent a formal offer and he went so far as to tell his tenants that he was avoiding me :)  The current tenants are moving out at the end of the month and I just saw that he listed the house for rent on CL.  So it seems like the time is ripe for me to ask him again;  considering his previous responses, I'm reluctant as I want to stay on good terms with him. (He lives out of state, but has occupied the house in the past)  So all that being said, at what point does my persistence become an annoyance and potentially damaged my (remaining) goodwill with my neighbor? 

Part two of this equation is the house itself. It's in need of some TLC and maintenance that has been deferred for too long. A roof leak that went un-repaired for almost a year has turned into an airborne mold issue. The HVAC needs some service, the windows leak like a sieve, etc., etc. For a time in the past, I was the property manager for this home (under the previous owners) so I have a pretty good idea of what I'm getting into if I were able to buy the home. It's not a great deal, but would cash flow neutral under my conservative calculations. There are strong emotional forces driving this interest, mainly the proximity to our house (12') and the ability to self manage and select who will be occupying it. It would also be a nice addition into my BRRRR portfolio.

So I'm curious to hear other's thoughts on this matter and other situations where your persistence paid off or where it damaged a relationship.