One of our local Petco guys said yes a snail is fine and helps keep the tank clean, the other (the same supposed aquatic specialist who said to feed 2x a week, 6 pellets) said we could get a snail but that eventually the betta would eat it. With our first betta this is exactly what happened. Bye-bye snail (can't even remember what kind it was, poor thing). I've seen on this forum that many have snails and they do well. Our tank is only a 2.5 gallon heated, filtered tank. Would a snail even be worth the mess it would generate? Thus far 50% water changes and the filter are keeping the water crystal clear.
And why does Petco not have standardized, ACCURATE, training of their fish folks? Some seem to really know their stuff while others clearly don't!