Well I removed those stickers on the visors and they left some adhesive behind. How can I get that off without staining or messing up the headliner?

I can take pictures so you can see what i'm talking about.

Naptha, or more commonly known as Colemen camping fuel, is the best stuff I've used, not too strong to affect plastic or vinyl but strong enough for most self adhesive.

I'd be tempted to try Goo Gone. I have used it on book covers, countertops and floors to remove stickers and it has never stained (itself, although the if you're taking off marker the surface needs to be non-porous) or left a residue.