Hay Day has a player-driven economy where millions of players compete for the best goods at the best prices in real-time . This means you may not always be able to purchase the item you wanted as it may already have been bought by another player.
In these cases it may seem as if you purchased the item by tapping on it, but the item will not appear in your barn and the cost in coins willnotbe deducted from you balance. The product will be greyed-out and a "Sold" tag over the item will tell you the item has already been bought.
If you purchased the item you will see coins being spent and the product flying up towards a barn icon at the top of the screen.