Actually, this might well be a feature but it's still annoying so I hope someone can give a clear answer one way or the other

When trying to buy from the store (or another player), I often get the situation myself and another player both attempt to buy, but they get preferential treatment... they can empty the whole store without me getting a single unit. I wondered if it was based on who got there first, but trying to press UP first often means I do it too fast and switch to SELL instead of BUY

What's the scoop?