I do disagree with this answer,

If I run

DECLARE @STR NVARCHAR(10)

SET @STR = '1, 2, 3, '

SET @STR = LEFT(@str, LEN(@str)- 2)

select len(@str)

SELECT @STR

The return for len(@str) returns 5 that would be '1, 2,' with no space after the comma.

If I copy the result of the SELECT @STR to word and have it show all characters there is no space after the comma.