When you say your sink base cabinet is 30" means that you measure 30" between vertical supports, he must have some trick up his sleeve. From your link's description section: "Min Cabinet Size: 33” More on reddit.com

Have a look around faucetdirect.com. They have a wide selection and brands to take you from basic up through higher mid-tier. Higher end than what they have will likely require you to find a local showroom. Is too hard to recommend anything specific as "nice" is super subjective. A nice sink for one person is 200 bucks, and 2,000 for another. More on reddit.com

If you are doing an undermount sink, it will have to be less than about 28" to fit inside the cabinet. If you are doing a drop-in sink, you can probably do a 30". dschang-online.com

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You can do a top mount. But, either it needs to fit the existing hole, or the hole needs to be widened (which is possible but can be tricky for the inexperienced). If you go with another undermount, in general, you'll want one with a bowl (not including the lip) that is very slightly larger that the opening, in both directions. (You also have to consider the corners, since some sinks and some sink openings have corners that are more square or more round). All of the lip of the sink should be under the counter. But, you also don't want the counter to be hanging way over the edge of the bowl--it will look weird, and it will be hard to clean. But, you also have to find a sink that will fit in your existing cabinet and can be attached properly to your existing countertop. In sum, you need to do a lot of research, looking at the specs for each sink, to see how it would fit with the existing hole in the counter. And, of course, if you plan to have the work done professionally, you need to find someone who can and will be able to replace the sink and do so properly. More on reddit.com