Choice of Graphics / Skin and Price

Yes and no.

There are plenty of people who prefer (or exclusively use) certain skins, especially for charms.
Whether or not that justifies a premium however depends not only on both sides of the trade but also the item being traded.

For example, I've seen a fair few folks look for certain skins (exclusively) in the grand charms even while still using naked skillers. Those are generally a dime a dozen and readily available in any skin you'd want. Having "the right skin" hence doesn't typically confer any sort of premium as you can just look 2 trades further down in the list and find the same thing at any time. The same is largely true for facet colors and such as those, too are readily available all over in any variation.

However, once you start looking at true top-tier items, be that 3/20/20s or 45 life skillers, those are already rather rare and hard to get to begin with. Getting them with the right skin on top of that is hence significantly harder as there's a good chance you won't even see more than 1 or 2 for sale at any give point in time. If any. In those cases, yes, skin affects price. Whether that's a premium though is a matter of perspective as at that level, the price tends to be established based on "what skin does the majority prefer?", rather than "what does my buyer want?". So your pricing doesn't move up/down much based on what skin your specific trade partner is looking for but simply based on which skins have higher value to begin with, simply because the majority wants those. If your buyer is looking for one that most people like the least then that's not a premium for you, that's just his luck because that'll be the cheapest one he can get, despite also matching his personal preference.

Beyond that, on a case by cases basis, you can always find people "who want that skin and who want it NOW!" who might then pay a premium so they don't have to wait 2 minutes for the next one even for more common items. But that's inherently subjective and special circumstance, rather than something you should expect as a rule.

Is it reasonable to say that in this game, finding such and such skins is no more difficult than finding any other and that the only real obstacle is purely statistical? Considering that, I am personally uncomfortable at the idea of hiking the price of an item just for that. It should be tied to how actually harder it is to obtain the specifically requested skin and nothing else. To me, that sounds like when landlords artificially increased rent prices at the beginning of Covid because "people spend more time inside". There wasn't actually any less housing available than the month prior and it was very obviously a shameful money-grab based on nothing at all. I don't entirely adhere to the Principle that increased demand in a system of supply and demand should automatically result in higher prices. It really should only be based on the actual obstacles of supplying that demand. This being said, I'm just an average guy that don't know much about anything so disregard if irrelevant.