It's a moderately hard, somewhat easy job and it's done all the time. The key is to get someone experienced in so doing. Ideally same people reinstall who remove but that's not always possible. Still it would be worthwhile to fly the person going to put it back on at least to observe the removal. If that's not possible then make sure lots of photos are made during removal and make sure all hardware accompanies the boat.
There are several excellent boat transport companies who handle these all the time and can advise the buyer in detail how it's done.
If I was advising the buyer, I'd advise them to make sure they were taking the full cost of shipping and of removing and replacing the bridge into consideration when buying. It is seldom that it makes sense buying an older boat to ship across country or countries but occasionally it does.