I took my time to visit the link address he sent and it seemed kind of legit, until he started insisting I pay the gas fee after he learnt I registered on the site.
Before completing the trade with me however, he reiterated that I must pay the gas fee before Tuesday, else he would spend the fund on something other than the purchase of my art piece.
In applying caution so as not to fall into the hands of a fraudster out of desperation, I tried to research the name 'roninsea' on Google and have asked a few friends if they have heard of any NFT marketplace with this name. None could confirm if the site is legit till today. Am conversant with Opensea, Rarible, besides these, please let me know if others exist.
I've never heard the name of that platform before. You should ask them to purchase the art pieces that they like from a reputable platform to avoid unnecessary problems and confusions. If they insist, let them go and never trade with anyone next time who asks you to register on a specific website just so that they can buy your art pieces.