Ordinarily, I'd strongly advise against buying a used OBi, but the issue has always been regarding buying from a stranger (via Craigslist or eBay or sewn into the jacket of the guy selling Rollecks watches). But, since you apparently know this person, and we can thus assume they're legit, then sure, go for it. But first, that person must delete that OBi from their OBiTALK dashboard, to free up it's OBi number/MAC for use on another OBiTALK account. So, if you can work with the neighbor to do that, then you're fine.