This has been suggested several times and the fact is that it will most likely never happened. On several occasions Xeadin has said that this server is trying to be as "vanilla" as possible. This would take out the "survival" factor and the ops don't want that. Don't take this the wrong way...I would love to have player shops, but it will most likely never happen
However, you can still make a shop, but without the "right-click" to buy signs. Lots of players make shops, but the work is manual meaning you have to be there to do the transaction. Another alternative to a shop is a melon farm. You can sell melon blocks at the market for 15 dollars. This is a great way to make money and it will also give you food. Good Luck