I said using == operator:

local id
Id = "BONAP"
Id = "BONAP                                      "

Select * from _samples + 'data\Customer' ;
where Cust_id == m.Id

Id = "BON" && no spaces but no match as well

Either field cust_id or m.id might have as many as trailing spaces you wish. During select trailing spaces would be automatically removed for comparison (also check SET ANSI).