To know if a seller is reliable, you have to look at the seller's rating. It's important to understand what JDirectItems Auction seller ratings and "Good/Bad rating ratio" mean.
A user of JDirectItems Auction can receive reviews as a seller or as a buyer on the platform. This user can therefore have good ratings as a buyer (i.e. the ratings this user received by purchasing products on JDirectItems Auction themselves), but have bad ratings as a seller and thus still have a positive overall rating.

In order to protect its customers, ZenMarket blocks all sellers with more than 8% negative ratings ratio and all new sellers with less than 5 positive reviews.
To see all positive and negative ratings of a seller, click on "Item page on JDirectItems Auction" from the auction page on ZenMarket (this action requires going through a VPN to access the site in Japanese).