Simple UDF Add Where Clause To IF

Hello,
I'm trying to add a where clause to the return value. Right now, the code counts the number of times a certain relationship type is used. Once the count is done it returns the value, also if the count = 0, then the return value will be populated = 1. So to take this a step further, how would I add another where clause where sometimes I want the count to stay at = 0. For example, I'm trying to add a clause where for certain org_ogt_code='supplier' the return value will always be = 0. I tried adding a where clause to the IF statement, but i keep getting error code 207. Its saids it an invalid column name, but I have the table join. Any help would be greatly appreciated.
Thanks
Bryan



CREATE FUNCTION [dbo].[ngcoa_get_multi_golf_count] (
@org_cst_key_ext uniqueidentifier,
@todays_date av_date)

RETURNS int AS
BEGIN
declare @ret_value int
select @ret_value = 0

select @ret_value = count(*)
FROM
co_customer_x_customer (nolock)
join co_customer (nolock) on cxc_cst_key_2= cst_key
join co_organization on cst_key=org_cst_key
WHERE cxc_cst_key_1= @org_cst_key_ext
and cst_type='Organization'
and org_ogt_code !='supplier'
and (cxc_end_date is null or cxc_end_date>@todays_date)
and cxc_rlt_code = 'Multi-Golf Parent'
and cxc_delete_flag=0

if @ret_value = 0
select @ret_value = 1

return @ret_value
END