Whos going to sell stuff for lower then a price you can always get?
For the Same reason you'd be willing to spend a 'Subscription Fee' to an elite shop... For Convenience.. Instead of Paying Money to go to an elite shop, take a small price cut to your bulk sale.. thats generally how it works in the real world... So say You want to Sell Stacks of Iron Blocks
If /shop buys your Iron ingots for $12 and you wanna sit there and Sell 9 stacks of ingots (1 Stack of Iron Blocks) you can Make $6912
So if I Set up a Sign Shop that Buys 64 Iron Blocks at a time for $6480 ($11.25/ingot) than You payed only $432 for an Instant sale of 6.5k
if you were looking to get Rid of 36 Stacks of Iron blocks (20,736 Ingots/ Messages) at Shop you could make $248,832
Or you could Click Max 36 times and still make $233,280 giving me a Profit of $15,552 and Saving you the time and your eyes.