Is there a way to know if a CF card is recognised as a fixed-disk mass storage or not before actually purchasing it?
I don't think so. You should agree with your dealer that you can return it if it does not work.
Also check
different Amiga forums. There are at least a few who maintain a thread with a list of compatible cards. Don't remember which, though.
Also; this is a problem when connecting the CF card with a PC? or when connecting it with the Amiga? or both?
Don't know what you mean. You can use the same CF card on both, the Amiga and the PC. Only after you formatted the card as an Amiga HDD, the PC will see it as unformatted. Removable is a problem for the Amiga only.