It is not reliable because the narrator is passing an unfair judgement and being bias towards the Jews by claiming that they cannot be trusted because of their appearance which is changing often.
The source shows a Jew holding gold coins in his hands and looking at it. This action implies that Jews are greedy. Also, the poster's background, is yellow in color. This is an important sign as yellow was not a popular color and Jews were forced to wear yellow hats and belts to identify them easily. These were to make them feel ashamed. Another sign is the map of Russia and the communists symbol. It is to show that the Communist and Jew had close links with each other. Germans, distrusted the Communist and labelled them as people who were out to cause trouble. With the same comparison to the Jew, it shows that Germans distrusted the Jews. Cross-referencing to Source 2, it states that "no one need be surprised if among our people the personification of the devil as the symbol of all evil assumes the living shape of the Jew" - Adolf Hitler Mein Kempf . This backs up source 1 as it is trying to emphasize the negative idea they had about the Jews.
This source is biased based on the provenance. It is produced by the Nazis and it is their opinion of the Jews. This shows biasness, therefore, it is not reliable.