String concatenation using LINQ to create a CSV/PSV string

The idea was good, but I think we could probably do something like below:

public static string UsingStringJoin(IEnumerable<string> sList, string separator)
{
    return sList.Any() ? string.Join(separator, sList.ToArray()) : string.Empty;
}

public static string UsingStringBuilder(IEnumerable<string> sList, string separator)
{
    return sList.Any() ? BuildString(sList, seperator) : string.Empty;
}

public static string BuildString(IEnumerable<string> sList, string separator)
{
    StringBuilder builder = new StringBuilder();
    foreach (string item in sList)
        builder.Append(string.Concat(item, separator));
    string buildedString = builder.ToString();
    return buildedString.Remove(buildedString.Length - 1);
}

If we have few strings to merge, probably use string.Concat(...) or string.Join(...) or for larger set of strings StringBuilder. Certainly your idea is good, I just want to show an alternate way to do the thing.