If you ask me the you should be able to buy and sell only basic supply such as:
Stone
dirt
sand
wood
glass
white wool
pumpkin
netherrack
torch
raw Porkchop
arrow
If you ask me this will be the best shop because the shop ruinds the value of items and its easy to get any thing you want...
no one buys from other players only from the shop
allso make a premium option witch will allow players to get more then just "basic supply" if you ask me the premium needs to be around 5$
it will ulock:
sponge
cobweb
piston
gold block
iron block
Brick Block
Soul Sand
Glowstone Block
Golden apple(should have a high price or players will just get god mod
)
Cake
Cookie
diamond(not as a block and its price wont be low about 6,000 crafts a stack if you ask me)
Gold Music Disc(id: 2256)
Green Music Disc(id: 2257)
and yes i wrote this commant late at night because im on a night shift and its boring!