I always thought it was strange with Achan that he stole garments - it seems like kleptomania.
Presumably they would be immediately identifiable as not being Israelite garments, perhaps in their quality, but very likely lacking in the fringes and blue thread.
There is no way he could ever have worn the garments in public, and he couldn't really trade them with Isrealites either, so what was he planning to do with them?