You know it's best to try the horn first. If that is really not possible, as you say, then in my opinion it's fine to order a horn: as long as you trust the source. A reputable dealer should allow you to return an instrument if it's defective or not as advertised; that's one safeguard. Do you have a reliable horn technician who can check the instrument for you when it arrives? I'd strongly advise that, too.
A trustworthy source for the instrument is imperative.
A trustworthy source for the instrument is imperative.