Non-combat interactions is one thing. The DM wasting the majority of the group's limited gaming time for the week on a non-quest, and doing it not because it will advance his story, or build his world, or show characterisation, but rather just because he thinks it will be funny (or worse, through some misguided notion that these things should be difficult and time consuming just because), that's another thing entirely.
When this happens once, it's annoying. When multiple DMs do it on multiple occasions, and think that this is the right way to go about things, it becomes a problem.
My gaming time is limited, and therefore valuable. If the DM has a reason to fill it up with a quest to identify and then sell a particular magic item, then fine. If not, then he's a bad DM.