Buying/Selling Complicated way

[g02h3LL]

This is complicated so you may have to read it a few times.....
This is not an auction!!!
I have 2 npcs, 1 that says buy and 1 that says sell. Its like a house. The person who owns it can touch sell and it says type "Sell amount" to sell. Then someone touches the buy npc and it says "on sale for Amount", thats the easy part. The hard part:
When someone touches the Buy and the owner has not touched the sell i want it to be like a bid. The buyer places a bid and it remembers the account name and takes the money away and then when the owner touches Sell it says the highest bid and accountname. If the owner says "Sell to bidder" it sells the house to the account that bidded the highest amount. Also if someone bids and then someone bids higher the person that bidded before gets there money back. Please help me!!!