When I buy an electrical device, I assume it's passed all the relevant consumer safety checks and complies with the regulations, as otherwise the shop would be breaking the law selling it to me (in the UK at least). I assume I'm safe to plug it in unless there's an absolutely obvious flaw (damaged power cable, for example).
Most people will go and buy a security camera or other device that connects to the internet and assume there's nothing to worry about if they're buying it from a high street shop. These things are sold as consumer devices in major stores, targeted at non-technical people. That should be enough, in an ideal world, for buyers to be confident they can connect them to the internet in the same way they can connect the microwave they buy to the power without worrying about whether it's safe.
OK, I accept that these days you can buy no-name stuff on the internet that probably doesn't meet safety standard (electrically or otherwise). That's your lookout and you should absolutely be liable for problems that result. But if you buy it at Currys? Argos? Well, in the UK consumer law says anything sold must be fit for purpose.