Weird Behaviour Of Imported Meshes

Bumblebee

So Im trying to convert weapons from a game (steam workshop) to highpolys to edit them in zbrush. The problem is that the obj (which the dev provides) behaves very weird when I want to edit it. For instance the mesh has hard creases when I turbosmooth it, the cut tool is inaccurate and buggyy. When I tried to weld the verts to get rid of the hard creases the mesh collapses even with standard weld values (see pic). Using inset or bevel for example is also very extreme. I was wondering what I could do to maker the mesh behave normal. When I imported it it was veeery small and I had to scale it up manually

danr

You need to reset the transforms after you've scaled it up 

utility panel > reset xform