This is a bit black and white. We do things all the time that have some level of risk, and draw vague lines about where this crosses into negligence. My cars brakes might fail, right? But it wouldn’t be typically called my fault - unless the chance was heightened because I’d not maintained it, or had been warned the brake fluid seemed to be leaking.

You cannot guarantee a robot could get items without paying. You can’t really guarantee anything in basically any scenario.

You can’t guarantee your card will work at the end of a meal or that your wallet won’t have been stolen, or while you were out someone stole all your money at the bank. There’s a chance those things happen, so do you never go for a meal?

Again there’s clearly levels where it is your fault, because you were negligent. If the robot goes mad and smashes up the place one in 3 times, obviously you can’t do it.

This is where we do things like trials, have approvals, etc so that we can make reasonable adjustments to lower downsides, plan things like insurance and then move on with our lives rather than never doing anything because it’s possible there’s a problem.