I am not a lawyer nor a German, but Wikipedia says that German law has no strictly liability [1], which would seem to imply that knowledge (or at least belief or a willful lack of knowledge) that the goods were stolen would be necessary to prosecute that crime. Is that wrong?
[1] https://en.wikipedia.org/wiki/Strict_liability_(criminal)
You are right in your assumption. § 259 requires intent. Usual interpretation is that the offender needs to know the fact that the good was somehow acquired illegally (but doesn't need to know any details). It's not enough to think of a possibility of such an action, they have to resign to the fact. (There are other obligatory characteristics that need to be fulfilled, but they are irrelevant to this discussion.)
Simply handling stolen goods is not a criminal offence in Germany.
(up to 5 years for handling goods that were stolen by somebody else)