When buying a used car, briefly how much money is negotiated?

I'm looking for a used car, and was wondering how much money is okay to be negotiated.
Right now I'm looking at a clean status 2017 honda civic (50,000km)and the listed price is 21000 after tax.
How much should I be able to negotiate down to? I don't want to low ball the price.

Added (1). I'm in Vancouver, Canada by the way

The best approach is to look for a comparable near your city, print out the advertisement, and ask if they can beat the price.

Not enough information. There are EX, LX, DX, Si, VTi-S, and Type R models, some are coupes, some are hatchbacks and some are sedans. Plus each is available with options, so the prices vary widely. You have to be more specific.

10% off asking price is a good stating point. Many sellers and dealers have already marked up their price to allow a buyer to "talk them down." Just check with KBB.com to make sure you are paying a fair price, even after you have negotiated a lower price.

Have your loan arranged before you step onto the dealer's lot. Look up //four square car sales// to see how the car sales deal is played.

The value of any item is somewhere between what the seller asks and the buyer is willing to pay.
As a buyer going into a deal you can always up your offer, you can never reduce it.

I would say to try for 20% off,
This particular one is priced pretty high, so unless it is a very fancy, like the Sport Touring or the Si model, I would be hoping to get them down to close to $15000.

Go ahead and do low ball them

Prepare by learning the market value of the car. Go to Kelley Blue Book www.kbb.com. Input all of the information on the vehicle and it will give you a value. If it turns out to be somewhere near $21,000 there will be nothing to negotiate.

You should be able to negotiate it down to market value.

10 to 15 percent is probably the best you can do.

Down to fair market value for the exact car & condition.

By the way, never in my life have I ever heard of a list price that included tax.