Pretty much, even though it seems like common sense that would need to be written in just to prevent headaches :p
Edit: If we make people have the sell option on some shops it will definitely drive buy prices up, but it will all be very close pricing wish across all shops. We would also need to make it clear that you must be cautious when letting players sell to you.
The issue here is that minerals like Diamonds and Iron are all hotly contested items and when an item gets priced at its lowest possible price (admin shop sell price), It will become quickly sold out either through players suddenly grinding cat xp (10-15k per hour) and buying everything out, etc.
Players will check half of the stores and would dismiss that the players with higher prices have brought all the diamonds and stuff, But I think this is actually due to stores having low buy prices causing fast sell outs while higher priced stores just sit there and wait till someone is impatient and slowly sell out that way.
The players who own shops do not have unlimited stock and aren't always able to meet the demand with their supply as they are players instead of bots.
Players with higher priced shops make money off players who don't check all the shops before buying or when everywhere is sold out. The Higher priced shops means less people buy from them, therefore they can always meet the supply and demand.
We might be able to add a rule or equity notice that players should not buy out cheaper stores to sell in their higher stores but I think that's about it.
There is almost no shop owner dumb enough to make their shop prices lower than admin store so don't worry, and if they are, they would either shut down in 1 day or change their prices back.