We did the shark swim ending at Dunn River Falls through DCL, and didn't have any sort of sales pressure at all. We met up with a guide who stayed with us all day through both legs of the excursion, and while she did drop not so subtle hints regarding tipping throughout the day, it wasn't bad enough that it ruined anyone's fun. More along the lines of "woe...I'm a broke college student trying to get off this island" kind of thing, and by then we knew tipping was gold on excursions. We had kids with us too, and never felt unsafe. After the shark encounters, we stopped for complimentary coffee and rum samplings, but there wasn't pressure to buy anything. They were proud of their wares, for sure, and of course they wanted people to buy, but not pushy. Dunn River Falls was a BLAST. We had so much fun. Our guide up the falls (different from the guide that followed us around) was a smaller statured woman, and total bada$$, climbing up it barefoot, and even hauled some heavy set, out of shape adults up the steepest parts. She was pretty amazing. We tipped her well at the end, and she was grinning ear to ear with the most infectious smile. I felt we were well taken care of all along the way.
The market at the port, while bigger than Nassau, I felt we had less pressure than the Straw Market in Nassau. We didn't even go into the Straw Market, walking straight through and got stopped at least 3 times. A simple, "no, thank you" does the trick. The market in Jamaica was busy, but mostly a non issue. We even stopped to pop into Tortuga's for rum cake, and stood around for a bit, and no one approached us.