It's funny how the practices that were once considered "the norm" are starting to become a little frowned on from a preservation point of view. I guess it was inevitable really as the toys we love get older, collectors become more mature/wiser and we start to think more about the long term impact of cleaning and restoration.
When I started collecting it was quite common for people to remove price stickers and do other similar "restoration" jobs. I'm sure you'll find plenty of threads on it on the forums from years back. Most collectors just preferred clean looking cards, there was no real interest in price stickers at the time..they were considered ugly!
Pulling bubble dents out with tape, goo gone/lighter fluid on stickers, using baby wipes to clean cards or even random stuff like polishing the dullness out of bubbles. It was almost encouraged at one point, everyone was doing it.
A good example of how things change: About 10 years ago I remember reading an article on toyfixer.com (I think it went by a different name back then) about how to polish the bubbles on carded figures using a compound sold by a company called "Tamiya".
This intrigued me quite a bit because I had a sizeable collection of carded figures at the time (well..for a 20 year old at least) and I thought they would appreciate a good "clean". I ordered a set of the polishing compounds thinking it was worth a try (I had plenty of figures that looked a bit scuffed and old).
I probably used that product on maybe 30-35 figures and while it did work, I never even really looked into what I was using (

). All I knew was that it was often used in other hobbies (model airplanes/cars etc) so I just figured it was safe. I guess I didn't see anything wrong with it at the time because the figures were mine and I also never intended to sell them..famous last words!
A couple of years later I sold up of course and off they went to eBay. I never disclosed the fact that I had used that polishing product on the bubbles when I sold them. It didn't even enter my head to do so if I am honest.
I've no idea how that product holds up over time or what the long term effect actually is on the plastic it comes into contact with. I'd like to think that it was safe and I didn't do any thing that couldn't be reversed or was damaging but I honestly have no idea.
In my defence, I did publicly post on RS that I was planning on polishing the bubbles on my carded figures before I did it and nobody even replied to the thread! I guess if someone were to ask a similar question now they would be asked all kinds of questions - if it was safe, had they researched it..what the long term effects were etc etc
Like I said, different times and a totally different mindset. Discussions about long term preservation weren't common at all and we all seemingly lived for the now and did what we thought was best at the time with no real thought to the future.
As with anything in life, you learn from your mistakes. I'd certainly never touch a product like that nowadays (even if it seemed safe) nor would I remove a price sticker from a card. The success rate of sticker removal never seemed very high to me and even those that got good at it would eventually **** one up at some point or another - that's when you think "I should have left it well alone".
There is a fine line between cleaning and restoration and it's quite often blurred by collectors. Some of the practices we've seen used in this hobby probably should be disclosed, many aren't of course but it's not always intentional or an attempt to deceive people - sometimes people just think they are doing a good thing to their toys or aren't really thinking that far ahead. (The craze of whitening stormies with harsh chemicals comes to mind!!)