Yeah, it's a fine art, and obviously if you have the acceleration of Messi you don't need as much of a head start to get in.
Offsides like Best's today, where one foot happens to be ahead of the defender, I just don't have a problem with. A lot of the time they won't be spotted and you'll score. When the margin is as tight as that a lot of it is luck.
Yes, he could be a better player and always bend his runs exactly right though, can't argue with that.
If it was purely down to luck then he'd be offside a lot less than he is, it's not luck, it's either laziness or ignorance.