Select item, press Buy…
Sometimes everything goes right, you get a confirmation right away.
Sometimes the button grays out but nothing seems to happen. Two minutes later, you find the purchased item in your transaction list. Or 2 of them, or 3 of them, if you thought something went wrong and clicked the buy button again.
Please have some dialog come up after one second or so telling that the purchase is in progress but slow. Create a funny text about junior traders still fighting off pirates or so, to keep people from thinking nothing was bought.