交易行一口价：明码标价的即时成交

local function sellNow(actor, itemId, price)
    setsysvarex("shopBin_" .. itemId, price)
    sendmsg(actor, 1, itemId .. " 已上架一口价 " .. price)
end
local function buyNow(buyer, itemId, seller)
    local p = getplayerbyname(buyer)
    local price = getsysvar("shopBin_" .. itemId) or 0
    if price == 0 then
        sendmsg(p, 1, "商品已售出或下架")
        return
    end
    if getplayvar(p, "GOLD") < price then
        sendmsg(p, 1, "金币不足，需 " .. price)
        return
    end
    setsysvarex("shopBin_" .. itemId, 0)
    giveitem(getplayerbyname(seller), 9021, price)
    giveitem(p, itemId, 1)
end

local function cancelBin(actor, itemId)
    if (getsysvar("shopBin_" .. itemId) or 0) > 0 then
        setsysvarex("shopBin_" .. itemId, 0)
        sendmsg(actor, 1, "已下架并收回 " .. itemId)
    else
        sendmsg(actor, 1, "无在售记录")
    end
end