When I finished the bit of the quest with the Auger, I got all my stuff back and got the bane of the undead spell from him, but I can't buy either that or the guardian circle spell from Collete, please help me.
If you're on pc, then you can console command the spells into your inventory. If you're on console, this a pretty common bug, & it's best to reload to a save before you did the ritual spell, save right before starting it, so you can keep trying. This happened to me on ps3 once, & I had to try it a few times, but eventually she sold them to me.
This is a known glitch. Colette will only have the spells available immediately after completing the quest. Once her store resets, the chance is lost. The problem is that the store will reset the first time you enter her store after a certain amount of time has past (or after you've quick saved, attacked her and quick loaded). The best thing to do is, prior to doing the test for the Augur, you talk to Colette, look at her shop, then you go to the Augur and once the test finishes, you run to her like crazy. Spell tomes should be there this time...
Happened to me too. Also, during the Augur's test I fought back against the Ghosts. When I passed the Ghosts kept attacking. I tried again. Disabled auto save and didn't fight back against the Ghosts. Just used defensive techniques. (Dragon Aspect, Become Ethereal, Greater Ward). This time the Ghosts stopped when I passed the test and I was able to buy Guardian Circle when I returned to Colette.