Ya keep your money. If you really need to check if he gets sea sick take a charter out and that will give you a better idea. Safer and will give ya an idea what you are in for.
Like they said, your buddy shouldn't get too seasick in the harbor since there are no swells. But if you're thinking about ending up with a fairly small boat, going out on a larger charter vessel might not give him the full experience. Some of my friends do fine on a larger boat, but get pretty queasy on my 21'. I agree on passing on an inflatable like that one.
You can go to the harbors and rent a kayak for around 10-20 an hour to get the feel..then look on craigslist for a yak...I just got mine at a yard sale for 200 bucks and it does the job.