Well, the vendors in JA will be far more persistent than they are in MX, that much is certain. You just have to respectfully (definitely not fearfully) say no thanks, and most will leave it at that. Some will not, but you just need to be firm. I've been a lot of places, and I have yet to find anywhere that has the "vibe" that Jamaica does.
I would consider ditching the Mobay part of your trip though, I've never cared for Montego Bay myself. I do recommend Treasure Beach on the south coast, it's a wonderful and peaceful town with great scenery and very little harassment.