I recently started buying ETFs. One weird thing I see is that Baader Bank is always a tiny bit cheaper. In the example below, Tradegate is 0.4% more expensive than Baader Bank:
The difference is not so high that arbitrage is possible, because all offer prices ("Briefkurs") are higher than all bid prices ("Geldkurs"). Still, it seems strange to me to see a consistent difference. Is this just a random effect (and hence not consistent)? If it is not random, why can that be?