Rare Candy and Ether are some of items that you cannot buy in the any game. They're quite precious and useful, though. As they aren't sold in any place, you have to think twice before using one. I would use my Ether usually in Elite Four, and in at the first time only. The Rare Candies I usually don't need, but in that case, I would use a Rare Candy if get stuck at an in-game battle (rival, gym leader, for example). The saddest part on using an unbuyable item is that you won't use another further when run out of them as they're limited. They'll be gone forever... So, here comes the question of the thread:

Would you like if some unbuyable items start to be available in shops? Which items could went on sale and which could still be limited? Why??? Do you think that if they went on sale, the game will become easier? It doesn't need to be in every blue-roof Market, but in special and unique shops, like the herbs. Also, I used Rare Candy and Ether as example, but you can mention other unbuyable items like Elixir, Old Gateau and White Herb.

Also, don't say that Pickup ability solves que Rare Candy issue. The chances of a Pokemon picking up a Rare Candy are extremely low to provide Rare Candies often.