AirBNB is just individual properties. We've used a few and not been murdered or burgled yet There's normally reviews so see what they say but they are just normal self-catering places. We don't use them much as prefer not to cook and clean on holiday but never had a problem with them. My only gripe is you are expected to clean and pay a cleaning charge. I've always used superhosts and places have been fine, good value, very clean. Can't imagine Venice being high risk.
its a booking platform so the only issue is that it will be more expensive than if you book direct with the owner. if you find the name of the property then google search it you might find a direct contact where it will be 5% plus cheaper.