It doesn't mean anything to me. It looks like a misspelling of either 'customer' or 'costumier' ( a costume maker or supplier). Some dictionaries list 'costumer' as an alternative to 'costumier', but I have never heard anyone say 'costumer'.

Maybe you mean "customer" a person in a shop who wants to buy something.Many people confuse these two words.

A costume(dress) designer.