I wouldn't say...alot of sellers, but there are some. Yes, you can relax and not be bothered. If approached, just say...you're all set...and they'll leave you alone. Actually, they're not allowed on the resort property. They travel the waters edge. Resort security usually monitors them.
Relaxing on the beach at CSA ,the answer is yes. The beach never seems crowded even when the resort is at full capacity. As far as vendors, and there are only a couple, besides the shell guy and cig. guy and you will learn them be how they sound,lol, they must stay at the water line and are not allowed to approach the guests while they are relaxing. If you are walking on the beach you will encounter a vendor or two and a polite no thankyou is all that is needed and they go on there way. Security is also VERY visible on the beach and they keep track of the vendors and everything else. One time my wife and I got talking with Elvis, the jet ski guy, and a security guard came by to make sure we had no problems, told him all was fine and that was that.
Go to CSA you will love it..