Are 3d assets purchased from assets website, say turbosquid editable? I want to save my time in modelling and sculpturing 3d model. I found some assets in turbosquid close to what I want. If I buy it, can it be edited in all aspect? How to know a 3d model in turosquid is editable? If there is no editable 3d model in turbosquid, any other sources to find editable 3d assets?
Yes they are, 

Re TURBOSQUID


  Do I have the right to modify Stock Media Products?
  
  Yes. You may modify them to make your Creations. Please keep in mind
  that no matter how much you modify a Stock Media Product, it still may
  only be distributed as a Creation and is subject to the rules of the
  Royalty Free License.


please read the TURBO SQUID licensing terms to be sure you can use them for your intended purpose.