C# LINQ - Extract Values of Dictionary<string,string> as CSV

I'm trying to output the values of the Fields dictionary (Dictionary<string,string>) as a CSV file. I need to put quotes around each value but when I use...

var values = string.Join(",", "\"" + a.Fields.Select(v => v.Value) + "\"");

...it outputs as

"System.Linq.Enumerable+WhereSelectEnumerableIterator`2[System.Collections.Generic.KeyValuePair`2[System.String,System.String],System.String]"

However, when I remove the quotations and use...

var values = string.Join(",", a.Fields.Select(v => v.Value));

...it outputs fine, but I need quotes around the values because some of the values contain commas.

        public void Print()
        {
            var csv = new StringBuilder();            
            var header = String.Join(",", audit[0].Fields.Select(k => k.Key));
            csv.Append(header);

            foreach (var a in audit)
            {
                var values = string.Join(",", "\"" + a.Fields.Select(v => v.Value) + "\"");
                csv.Append(Environment.NewLine + values);
            }

            File.WriteAllText(AppConfig.CSVFilePath(), csv.ToString());
        }

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