Bukkit

Players are able to put down a sign to sell items and when the put up the sign the amount of material specified is deducted from their inventory.

(override for server shops).

That would allow offline selling and buying via signs.

Would be cool if the last line would show the price.

EG:
[SELL: 64]
cobble
dredhorse
price: 1000

so first line sell and amount you want to sell (which is still there)
Second line what you sell
third line who is selling
4th the price.

Also nice would be the option to whack a sign with a stack of cobble in this case in your hand to increase the amount of blocks you can still sell.

sign support is a popular request.

I really like the 'whack' idea which you've presented here.

Actually, I like the overall way you have this working... Baring better suggestion and complications, I wouldn't expect my implementation to be too far off from this.

I'd love to see this. But in a way more basic way.

Like

[Sell]
Item
Amount
Current Price

And the current price could be updating dynamically per current value

@nanashiRei: Go

so you don't think it's important to know who you are buying from?

And I actually didn't consider having a 'set' price via the sign. I assumed that DonRedhorse meant to display the server determined dynamic price. Reading it again, I think DR may have meant a set price.

I currently intend to have signs use the dynamic price (but I haven't even started writing the code yet :)