You can only go back in time the day the time machine was created. So if you make a time machine and wait 30 years you can only go back 30 years to the day the time machine was created.
We do the same thing here at work with summer hires, We ask them to grab us a left handed spike maul. They will look for like 30 minutes come back and say they couldn't find it, so we tell them to go ask the foreman. classic
Who would buy a 2013 with 30k+ miles on it? Furthermore, how the hell could someone buy a brand new car, put 30k miles on it, and trade it in for another within before we're even out of it's evena year old?