SORRY FOR THE EDIT:
I was talking about RAW copies (Unlimited to be honest), take care, prices of graded cards are always higher, and this is a fact for every market.
Differences can be quite higher depending on the card itself, the ageing of the set, being a 1st edition etc…
If you have more details of the items you’ve seen or you want tell us about them, or there might be a misundersting
This is partially true, conditions may not be always correct, I had a terrible experience with cards from cardmarket (not for other items thanks god), but with the time-graphics and (some) of the cards already being pictured by the sellers, you can in fact have an idea. Just don’t trust that site 100% as you shouldn’t trust me 100% cause I’m not giving you an objective answer.
Hating aside, I recommend you to always ask for pictures on CM if you happen to use it, your NM might be different from the seller’s NM and you’ll end up not getting what you paid for.