It is easy for a practitioner to be decieved.
The tree of life mirroring the tree of death image isn't quite accurate. It's more like there are good and evil spirits attributed to each sephirothic level. So say you try to contact the sephiroth of tifferet, which corresponds to the Sun, well there are good and evil spirits attributed to each degree of zodiac, so depending on the nature of the request and the nature of practitioner, the mage will call down either good or evil spirits.
A lot of people assume planetary spirits are all angelic, but this is not the case. Even the Old Testament records instances where YHVH holds a meeting with evil spirits and sends them to Saul.
And see pic related. Agrippa's planetary seals contain an intelligence of good and a spirit of evil. So the evil spirit will do evil works, but the good intelligence will try to work it out for good purposes - such as the mage realizing the futility of chasing his vices after he has obtained them.
But if a mage just randomly calls down planetary spirits, and asks for evil works, he will certainly draw an evil spirit rather than good, which is likely the case with Crowley who has a lot of evil works attributed to him - these are not the works of angelic beings.