I'm sure they always put some thought into the sets. I've seen many decently thought-out sets that can catch some lesser-experienced players off guard if they are not aware of the opponent's pokemon's available moves and abilities. I remember the first time playing through Ruby. I got to Steven, and had no idea that Skarmory could use Spikes. Throughout the match, it was something I kept forgetting about because I also had to stay concerned about my Blaziken's HP. Every time I switched out to something else cover for Blaziken while I healed it, Spikes took out some HP, and sometimes even KO'ed the weak pokemon that I had.
On a side-note, Sand-Attack can and always has been annoying, at least for me. Especially if the pokemon is faster than you.