No problem about the "noob" question.
Yes of course its possible. The same holds true for virtually every car there is.
CSL's are just more prone to it, because when you can earn 30k $ with a few mouse clicks.. alot of people get greedy.
Yes, the mileage gets stored in various modules and cross-checked at startup. If they mis-match a indicator lights up. See
Tamper Dot.
If you don't have the tools you can also ask your local bmw dealership to do a "used-car-check" for you. They can also look up the cars repair history, if its been serviced by a bmw dealer in the past.
You can cross check the BMW Repair History with the cars service book if they match. Also if there are any MOT/TÜV Records where the mileage gets recorded, check those too.