I went on a singles cruise in October and got a great cabin mate. It was sheer luck. I also met my 2nd cabin mate on that cruise and she asked me to cruise with her so I did. The key is communication and compromise. Im not a neat nick, and my clothes end up in a pile sometimes she didn't complain. Im also a night owl, but I am trustworthy and not a drunk.
Some people go for romance, and to hook up others do not, I did expect to but found romance on my first cruise, but not on the second. No big deal it's not the reason I travel and Im very picky. Some guys will pursue you if your not interested be polite but distant they usually get the message and move on to someone who might be interested in return.
I've seen some horror stories one lady roomed with a drunk she told her off but the drunk gal didn't even remember so I suggested she speak to her in the morning when she was sober. They seemed to make up later as I saw them having fun together on the ship.
As far as the agencys are concerened all they do to match people is look for smoking preferences or non smoking. They don't care about all the rest. THey might not even tell you who your cabin mate is but you can post on the precruise message/chat board and maybe find out. I have made many friends and future travel partners. Like minds attract and there are groups within the groups. I keep in touch with many I've met and Im planning new trips. E mail me any questions I will try to help.