First of all, you need this script.
/script local function buy (n,q) for i=1,100 do if n==GetMerchantItemInfo(i) then BuyMerchantItem(i,q) end end end buy ("Telaari Grapes",255);
Then go to a vendor, Put the item you wish to buy in the "Telarri Grapes" area(replace it) and click the macro
The grapes are just an example(I have a stack of like 3k grapes, but sometimes it will make more than one stack of 255+ or a little * which means more than 255)
This is best to do with food / arrows as you will not need to buy more for a long time. You can buy weapons etc that will make it a stack of 255 but the stats do not stack unfortunately.
Here's a screenshot.
http://img218.imageshack.us/img218/2552/exploitpi0.jpg
If this is a repost QQ I don't care delete it or w\e it is that you do. Also I probably won't be answering any questions so either you understand or you don't , sorry.