White smoke is never good. No point getting involved with a car that might cost you a large proportion of the initial cost.

A good trick i read about is to start the car up, and pull the oil cap off and see if any smoke comes out through that. If not then thats a good sign.

However, if you're set on this one, get an inspection done at a subaru specialist workshops (stechnic, mms etc) and see if it's anything major.