Generally speaking, any keys being sold on ebay are used/coded keys that have been kept back when trading a car in, so that a small extra lump of money can be made when selling them after fitting a new uncut blade.
This means that the engine's ECU "dead lock" transponder has already been coded, and it has been said that you can not always successfully recode these transponders. The only way to sort that out is to buy a new correct version of transponder pellet and fit it into the key, easy if it is a folding type key.
Always a very smart idea to get hold of a second key though!