If a cw has an estimated value of 30 million, what is a fair offer of CSC please? Also, how do you know how rare a cw item is? Many thanks in advance.

There's no way to really know how rare a CW is, you'd have to ask about the batch numbers and if it was private or not (and if there were public copies). Even so, being rare doesn't always make it valuable or in high demand (I've seen people trying to sell spare copies of private items and having trouble).

You can look up and others to find the current sP value of CSC. You can usually buy it in Advertising for anywhere from 3m = 100 CSC up to the current shop search rate. 30m is about 900-1k CSC

Thanks so much . Very helpful information! :)