Here are some examples of my own stuff I've refurbished, plus a TG-16 and a Saturn for forum members. Click the links for pictures.
Do you hate those silver rental void stickers? I can get those off. Did you find an old PS1 glossy cardboard longbox with price stickers on it? Even if someone else peeled some off I can get the leftover gunk off without damage. Again, these are cleaning the old glossy cardboard longboxes directly, this is not me just replacing a jewel case.
Most marker I can get completely clean as long as it is not on a paper label. Front of NES cart on textured area. Unfortunately I haven't figured anything out to help deep scratches yet. Thanks Video Express for hacking the game up with an engraver.
Occasionally the plastic will still hold a slight ghost, but its still a dramatic improvement.
SNES pad before and after refurbishing. This had been sitting in a bucket in my friend's garage for years. Several PS1s that had also been sitting in the bucket. Closer shot of one.
Here are some systems other systems I cleaned up. Turbografx-16, Saturn close ups 1 & 2, and Jaguar close up.
I do a full teardown, not just a wipedown with a damp sponge.

Shoot me a PM and we'll hash something out if you're interested. Let me know what you have and we can work out a deal with you covering the shipping both ways. Barters for services are welcome. I have tools to open systems and carts as well as a scale so I can help approximate shipping beforehand.