If you win two stations, and you bid higher than one than on the other, the highest bidded one will go to you. If you win two stations and you bid the same on both, you get to choose.

 

If we win a bid on a shop, how long will we have that shop? I'm assuming until the annual Skyblock reset?

 

(Source: https://www.ecocitycraft.com/forum/threads/175098)

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EDIT: I actually managed to miss the more obvious location.

(https://www.ecocitycraft.com/forum/threads/skyblock-shop-auctions.175207)

 

So they are auctioned every month. Awesome.