Even though I have several alts that have nearly all professions maxed out, I never unlocked all nine profession slots on any character. The reason? Because the 8th and 9th slot cannot be unlocked through normal gameplay and require you to acquire higher quality profession assets which only come from the various random packs from the cash shop. This has always annoyed me and I refused to support it out of principle.
However, other day I decided to finally give in after all, specifically because I felt that I was wasting resources by only ever getting rank 1 results from a specific mission, and the assets I needed were actually going for fairly cheap on the auction house.
Looking at it now, I almost feel a bit silly for handicapping myself for this long when I could have simply bought the things I needed from another player all along. Even better, since they don't bind on use, I can now send them around to all my alts and use them to fully unlock the profession window on all of them.