does it ever show being in for service on carfax? If it did, they would record the mileage. Also, if it is showing no service, then that would back up the fact it may only have 5k miles on it. Also, I am guessing it is a 1 owner car? I would find it hard to believe it has only 5k if it is a multiple owner vehicle. And there are plenty of folks out there that have low mileage cars. I know a lady who comes in for regular service on her chevy pickup and it is 15 years old and only has like 10k miles on it. Her husband died, she doesn't want to sell it, and she only drives it to keep the oil changed and such. So there could even be some sort of back story as to why so little miles. I would just ask the seller why it only has 5k, see what he says.