was over at my sisters house helping her with something . while there i took a look as her vehicle . i checked the oil and it was dark and about 1/2 quart low. i asked her when she got her oil changed last. she said she just got it changed at the toyota dealer a couple of days ago. i looked a the reciept and she has put about 60 miles on it since. looking at the oil i am suspicious if they changed it or not. two things got me. the color and the 1/2 quart down. i told her my suspicions and she asked how do we prove it? So that is the question. how does one prove that oil was never changed ?