More information is really needed for a detailed opinion. What model Kitfox? What model Rotax 912 engine? Etc, etc.
However, in general, it would be wise to use the same practices used when looking at purchasing any airplane. Get the "N" number and do a search for it and it's data from the FAA.
Link Look for liens. Look for damage history. Inspect the logs for completeness and general content.
Depending on your mechanical aptitude, you can do a fairly thorough pre buy inspection yourself. If you are not so inclined, I would recommend having an A&P, not associated with the owner, do an inspection or evaluation of the airplane.
Don't get emotionally attached and be prepared to walk away. (this is the hardest part)