Rick, it does return the space at the end:
DECLARE @STR NVARCHAR(10)
SET @STR = '1, 2, 3, '
SET @STR = LEFT(@str, LEN(@str)- 2)
select len(@str)
SELECT @STR
SELECT RIGHT(@str,1) -- returns space, not a comma
BTW, I got it wrong too.
/* Anything is possible but is it worth it? */