From: R4nd0m
Basically they do this:
http://villavu.com/forum/showthread.php?t=68247
Also we do not take money in fact it is against the rules rather we write scripts so others can learn.
I imagine this kind of script will basically require the user to input all the merching data (buy price/sell price/item) then it just flips it.
EDIT: Post above explains :P
All you would need to input would be the items, percent to increase/decrease, and how much to add/sell. Although yours would work just fine :)
The reasoning is that it would buy for like +15% and sell for -15%, find those prices and the margin, add/decrease prices (to decrease profit margin but also resulting in faster flips) then buy the items for this new price.