Regarding the luck on throws - I think it comes down to the environment. In randori, where you're both playing a throwing game and there's no other variables, 1000 times out of 1000, the inexperienced person his not going to throw the judo black belt. Maybe one time out of 10,000 they will. I know this because I am that inexperienced person, and I've also watched others.
That said, if we're now allowed to strike as well, if the inexperienced thrower is a better striker and knows the basics of some throwing throws (or at least balance), they can use strength to throw them. This depends on how good their striking is though, along with their own balance and timing.
If we now assume that it's not in a dojo setting, but in a street setting, it's an entirely different story. When the fight isn't starting on even terms to begin with, you're busy trying to position yourself safely and being wary of extra people coming out or weapons coming out, it becomes a lot easier to fall prey to a 'lucky' throw.
That said, if we're now allowed to strike as well, if the inexperienced thrower is a better striker and knows the basics of some throwing throws (or at least balance), they can use strength to throw them. This depends on how good their striking is though, along with their own balance and timing.
If we now assume that it's not in a dojo setting, but in a street setting, it's an entirely different story. When the fight isn't starting on even terms to begin with, you're busy trying to position yourself safely and being wary of extra people coming out or weapons coming out, it becomes a lot easier to fall prey to a 'lucky' throw.