I recently bought some knives that did not come with sheaths. There is a Amish guy down the road from me that works with leather and I was going to get a quote from him about making me some. Another friend of mine said some types of leather will cause the blades to rust. Is this true or is it just how you take care of the blade. I have some knives that are stainless but others are not. Is there a certain type of leather to use or is it a case of leather is leather is leather??

Good question.Ideally sheathmakers should be using veg-tanned leather.Your friend was right in that some cheaper sheaths are found to use Chrome tanned leather which is not good as a liner for sheaths or holsters.
First and foremost knives and guns should not be stored long term in thier sheaths and holsters, because any moisture the leather has in it or has absorbed will be in contact with the steel, and even stainless will rust and discolor.
When looking to have a sheath made,the maker should dye and seal the inside and many don't.Unsealed leather will wick up moisture much quicker and the fact it simply is taking shortcuts.The sheath should be firm and offer some retention even without the aid of an additional strap.ALL fixed blade sheath should have welts ( a strip of leather sewn between the layers to protect the stitching) and if it doesn't have one, walk away. There should be no metal (snaps or rivets) coming in contact with the knife.Dave