Whether or not a car with that many miles on it is still a good buy will depend very heavily on how the previous owner(s) treated the car. If people kept it in good condition, it might be a good buy. If they didn't, or if it's been in a serious accident, or if there is something wrong with it, I would avoid buying it. $8000 is a lot to pay for a car with 140K miles on it...even if you could talk the dealership down, I would not buy it unless the car is in absolute top condition.

Find a mechanic (not a dealer) you trust check the car out. If you search around, you can probably find someone who has experience working on hybrids. The honda civic hybrid is a little less high tech than the prius; it's more like a regular car, so you will probably be able to find someone.

Also, I would advise to test-drive the car at least 10 miles (the dealer I bought my 2003 HCH from let me drive mine over 20 miles before buying it), and calculate the mileage. Are you getting the mileage you're supposed to? If you can't get over 40mpg, don't buy it...for $8000 you can pick up a Toyota Corolla or Honda Civic (non-hybrid) with low mileage, and those cars can get 35+mpg. Some of the German cars that run on Diesel also get outstanding mileage.

I would emphasize...for $8000 don't buy a car with that much mileage unless it is in absolutely top shape--if a mechanic checks it out top to bottom and finds no major problems. And check CARFAX for accidents too.