I’m also not convinced it’s an authentic 3Rensho. I can’t make a definitive judgement but here’s my thinking:

why it’s possibly not a 3Rensho: missing the engraved seatstay caps, offset fork, and engraved “SuperEnds”. Lugs aren’t the “katana” or “modeulo “ styles common on 3Renshos. Most 3Renshos in the USA came through Ariel Trading aka Yellowjersey, and those typically have the engraved seatstay caps.

why it might be a 3Rensho: they did make more “generic” frames that didn’t carry the features listed above. Also, very early examples from the Cyclone era pre-date the details we associate with 3Renshos. I have seen Cyclones with the same fork crown design as this bike, but it’s not unique to Cyclones.

verdict: for $150 that is a gorgeous bike and. Great deal, regardless of provenance. Once you buy it, share a photo of the serial number or other identifying stamps on the BB shell and maybe we can definitively identify it.