How do I get neighbor to sell when he doesn't want to sell

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I owner occupy a duplex. Next door property is also a duplex, owned by a retired couple. I've asked them to sell it to me, that I would pay market price because the location is convenient for me. A year later I brought it up again, even offered to 1031 one of my higher value SFR in the same area. Basically get a soft no, "not interested at this time", never even asked me for a dollar amount. I paid 68k for my duplex 2 yrs ago before I rehabbed it, they paid 76k for theirs 5 yrs ago. Both were severely outdated but in a gentrifying area. his is still a pretty rough, low income property Any reasonable suggestions, creative ways, ideas on how to convince them to sell? Not sure typical seller financing would interest them, doesn't seem to be very popular in this area.