Generally a custom order can only be returned for replacement, such as when it was damaged or somehow defective when delivered.
Many companies have strict policies regarding non-refundable deposit and non-returnable goods that have been custom made. Other companies have generous return policies in which they will accept returns of nearly anything, as a gesture of good customer relations. LL Bean and Nordstrom are among those famous for such policies (because they are so very rare). Another site which is pretty lenient about their custom clothing return policy is SoldierCity, which offers custom military clothing.