I looked at blendswap.com where there are models that I want to make walk along a wall in this level. AFAIK I can take this file and sell it or did I misunderstand licensing?
Th CC-BY 3.0 terms are pretty clear in this regard:
So yes, you can sell the CC-BY work from someone else, unmodified or modified. You just have to credit the author. And you don't have to release your work under the same license (the CC license which requires that is CC-BY-SA).
The BSD licenses (there are multiple of them) also allow you to use the work, even commecially and even under a different license. The difference is in the attribution clause. All BSD licenses demand that you give credit by including the original copyright notice. The 4-clause license (which is rarely used nowadays) also demands that you give credit in any advertising material:
But beyond that, you have to be careful with giving any more credit than that, because the 4-clause and 3-clause BSD-licenses forbid you from using the names of the original authors to promote your product:
The 2-clause BSD license doesn't contain this term. It only requires that the original copyright notice with the license terms stays intact.
Note that it is OK to state that the BSD license terms only apply to those parts which were made by the original authors, not to your modifications. Many proprietary software companies do that.