I thought the don't clean chapter was a joke. If it was serious, I guess it sounded so silly, it just had to be a joke?

Same as most. I don't clean if I plan to trade or sell, unless it's a light removal of built up grunge.

I clean chips for my own collection, if the mood strikes me.

I use Siloo/CRC Glass cleaner which is also marketed as a label and tape remover, will not harm lexan, so that means non-abrasive. It does not discolor Gold hot stamps, which would be something to watch for with any cleaner. Some will change gold foil to silver in seconds.

To each their own.