もっともらしいじゃないです
尤もらしいじゃないです
mottomorashiijanaidesu

Desu Copula
i-Adjective
Negation Auxiliary

The polite negative form of もっともらしい

1. Wouldn't you say?; Wouldn't that be reasonable?; It seems likely, doesn't it?

Negative
Polite
Casual Register
Usually Written in Kana