So, you want to shop a cruise or a resort. You’re thinking it would be a great vacation for you and/or your family. Wrong. Cruises and resorts are two of the most detailed shops there are. They do pay very well in many cases, but they require a lot. You won’t be relaxing, you’ll be working. Like the amusement park shops, some of them may allow you to bring your family, so you’ll essentially be working so that they can enjoy themselves. Do not ever schedule a shop like this on a vacation. It’s simply not doable. Mystery shopping is a job.
I only know of three companies that shop cruises. I’ve heard of several more, but after more than ten years of shopping, I can only confirm three (not counting day cruises or timeshare shops [timeshares are generally NOT worth doing – more on that later]). I’m sure there are a lot more, but these are not shops that are generally advertised. Cruises and resorts are “Don’t Call Us, We’ll Call You” shops. The funny thing is that they come from the most unexpected places. I was on a resort shop, and a small mystery shopping company that I do reimbursement-only restaurant shops for called to see if I could pick up a last minute one near my home. Wouldn’t you know it that I was 1700 miles away on another shop! They haven’t offered again, but I’m still holding out hope! I would never have expected the call to come from them. 
Do all your shops well! (You should be anyway.) You never know what other clients a company might have. You’re not going to get the call to shop a cruise or resort until you’ve proven yourself. That term can vary from company to company. I’ve been working solidly for two years for one that I know has cruises. I finally asked and the scheduler said that cruises almost always go to shoppers in New York or Florida. I’m still looking for that elusive cruise that leaves out of Seattle or Vancouver, BC!
The resorts have been great, but it was eight years shopping before I was offered my first one. On the last one, the kids went with us. The pay did not cover everything, but would have if there were only four of us (we are six). I spent a lot of time away from them, but they had a blast. It was a vacation for them while I spent hours writing narratives. It was all worth it.
The bottom line is that you should not get into mystery shopping for the advertised cruises and resorts because the likelihood of receiving one in your first couple of years is pretty slim. Unless you have a hospitality industry background or degree, or have demonstrated over time and quantity that you consistently perform above the grade, these shops will continue to go to those who do. Take the other shops and consider these an unexpected bonus should it ever happen.