Longtime Reverb buyer and seller here. The company is legit; they were originally a spinoff of the Chicago Music Exchange retail store (you can kinda tell, their website listings are slightly similar in form), but are now a subsidiary of Etsy.
The duplicate listings you see are often from Japanese sellers; they do the same thing on eBay. They often list the same item at least twice, one with a higher price but free shipping, another with a lower price and separate shipping.
I would say the best bet for both platforms is to only buy from sellers in the same country as you, that have a minimum number of good ratings, take the time to completely describe the instrument, take detailed photos, etc.
That said, you can get a lot of bargains from Japan on the proxy buying site Buyee.jp, which translates listings from their own JDirect auctions / sales platform as well as Mercari, Rakuten and Rakuma, so you can find both used and new items that can be harder to find here (Fender Japan, older Ibanez etc) including store brands like CoolZ and History, both made by Fujigen. The interface is…quirky, with slightly different category groupings dependent on the sub-site. Buyee handles the packaging (god tier bubble wrap skills) and shipping and it often arrives in under a week. Never had an issue with them!