well if one were to buy car in cash, I'm sure he/she have all the records /source of the $$ 

35k is a small figure, it possible not to have a trail. Ah kong ah mah their monies maybe kept under the pillow, you can't say they must keep money in the bank. Some more you can always say this relative give 10k, that relative borrow 10k. I think it cannot be proven wrong or cheating.

If one buys a car with cash for 150k or so, then it's different story.