Thanks for your feedback!
As Lylirra mentioned [url="http://us.battle.net/d3/en/forum/topic/7004693267#14"]here[/url], we're definitely aware of the frustration vendoring the wrong item can cause for players (I've done it, myself). We strongly urge players to use caution whenever selling items to a vendor, and to take advantage of the Buyback tab in instances where an oversight occurs, but beyond that, we have no immediate plans for an additional layer of protection.
Not having an item lock is as dumb as not having seat belts in cars, not labeling poison...poison or having signs at train tracks indicating trains.
Ya, its a simple mistake and people should always take personal responsibility, but i can't imagine what small effort it would take on the part of the designers to implement the item lock compared to the loss a player can experience from accidentally vending "gg" gear.
This response is totally unsat.