One of the posters said that "professionals don't hit a horse" I respectfully disagree. A good trainer WILL hit a horse when it is appropriate to do so. Usually as a response to direct, overt, aggression. It should never be done punitively, or just to make the handler feel better, but there ARE times when it is an appropriate response.
I also agree (mostly) with Horsiezz in regards to trying to fix it yourself. Of course it is best to know when you are in over your head, and when you are, to seek professional help. But another thing to keep in mind is that respect is NOT transferable. The trainer may be able to cultivate it in 5 minutes. That doesn't mean the horse will view you with the same respect afterwards. If you really do need to employ a trainer to establish respect in the horse, please get him to work with the horse AND YOU afterwards, so that you will know how to cultivate the same respect.
Good luck.