「騙された」と言ってしまえばそれまでですが、「うまい話」に乗った当人であることは間違いありません。

「」、「」。

It's easy enough to say "I was scammed," but there's no denying that you're the one who fell for a "too-good-to-be-true story."

Literal

"Deceived" [quotative-と] say-[if-finished-てしまえば] that-is-the-end [copula-です-but-が], "good-story" [target-に] rode person-in-question [copula-である-nominalizer-こと] [topic-は] mistake exist-not [polite-ません].

Formal and carefully argued. ~と言ってしまえばそれまで is an idiomatic structure meaning 'if you just say X, that's where the discussion ends (but there's more to it).' The verb 乗る ('to ride') is used metaphorically for 'fall for / take the bait.' 当人 is a formal word for 'the person in question, the very one.' 間違いありません ('there is no mistake') is a polite-formal way to assert something as undeniable.