[Eighty Swords]

you should require every skill in the game to make the knife and it should be noobied imo, then the price wouldn't go for cheap and the purpose wouldn't go bad

I wouldn't quite suggest you need EVERY skill gmed... if it's meant to be a craftable then you should just need the related craft skills to make it.

Or make two different versions. The cheap one that you can craft at lower levels of all skills (lets say 70 in all) and sell to other people, or use for yourself.

Then, a newbied one that you can only craft for yourself once you GM all trade skills. Takes expensive ingredients and possibly things from quests or monster drops.

I like this idea. Or the first one you make is linked to you and noobied (as a reward for GMing all the required skills), all further items of this type are not noobied so you can sell them. This way as Shade said there will be some point to killing people carrying them and they'll still have value since not everyone has all the crafts gmed, but you have the incentive to do it if you really want one of these noobied.