Correct me if I'm wrong, but as far as I know, Cazador has social influence he can use to avoid getting into too much trouble. Also Baldur's Gate might not be the biggest city, but I'm pretty sure it gets plenty of visitors from other areas, some of which can be conviniently snatched before they have a chance to make themselves known. Their first stop would probably be a tavern anyway. I definitely do agree with you when it comes to numbers, though.
I don't think either of those things solves the problem.
Astarion tells us that most people don't know Cazador is a vampire lord (how true this is, I'm not sure - apparently some folks know it quite well). If Cazador is trying to keep his status a secret, then needing to use social influence to cover things up is already a failure. Someone has caught on. Someone has acquired knowledge they can use against him. He's been forced to spend some of his own influence to fix things - and who else knows now? It's not a good situation.
Preying on visitors also isn't a very good idea, I think. They're just as likely to have people looking for them as anyone else - in fact, it might be even harder to figure out whether they have powerful friends or family or employers back home, since there's not much opportunity to investigate their background. Wandering vagrants? Probably not a problem. Sailors? Not a bad target - it's a port town, lots of them arriving or departing daily, and I doubt it's unusual for a few to go AWOL while ashore. Criminals on the run (like our squiddy friend eats)? A bit more dangerous, but neither they nor their friends/families are likely to approach the authorities. Those are the groups I'd expect to be targeted. But not too many, not too often.
