I think BianchiGirl is right about it being a 'Terry' style bike, though the angle of the photo obscures it. Nice job of CSI-C&V work there!
Doubt the seller was trying to hide this as he doesn't sound very sharp.
Terry bikes were designed by Georgena Terry back in the 80s, and her idea of a frame that took a small (24") front wheel, so the frame could be small without 'toe overlap' of the front wheel (the usual problem with small frames) was copied by many companies. At 5' 3" you might fit on a regular small road bike with a 19 1/2" or 49cm frame, but the Terry style might work well for you, too.
Shogun was a made-up brand name, built for and distributed by a company in Seattle. There were a bunch of such companies in the 80s. Japanese bike production at the time was in its heyday and even fairly basic bikes from that era can be of surprisingly good quality. Shogun is not as well-known or documented a company as (say) Miyata, Fuji, or Centurion, so there don't seem to be any catalogs from the era around. They used a numbering system for their models, at least some of the time, higher numbers being better models: 200, 400, 500, etc. Apparently they changed that to names so who knows whether a Samurai was the entry 'soldier' level bike or the top 'general' model?
Actually seeing downtube shifters on this bike suggests it's at least mid-level. I would suggest having a look at this bike, esp if you could take a knowledgeable friend along. While there are a few people who know and want this style of bike, I'd say it's unlikely this seller is going to have people clamoring to buy it. (Also a hard core Terry bike fan likely wants a real Terry.) If it looks good, fits you, etc, and you can get some kind of idea of condition and work needed, you might give the guy an offer of say $150 or $200, see if he bites. If he says it's a $400 bike say, 'Yeah, fully rehabbed, in Portland, on a nice day, which I hope you have.' And be prepared to walk away.