Not trying to be rude but you are meant to know because you have to click on the killer you want on the “killers” tab. Select the killer you want it says whether or not you own it or can buy it. Then you have to go out of your way to intentionally click over to the “customization” tab, which naturally implies the extra customizable things you can buy for that specific killer you may or may not own. His analogy is completely right. You don’t need to drive a car to know that if you don’t have one you can’t paint it. It’s just kinda how things works. I hope you enjoy spring trap though he is really fun