Quoting Corinthians

Imagine reading a letter where the writer is engaged in a heated debate with someone and repeatedly cites their positions, but never uses quotation marks to indicate that he is quoting them. This is precisely what we find in 1 Corinthians! Paul frequently quotes certain factions within the church and then proceeds to correct their faulty thinking; but he rarely explicitly tells us that he is quoting them. This poses a significant challenge for interpreters of this letter. How do we know when Pau