Haggling on a car is not unusual. But what about the tires?
There are three things that make tires an especially nice target for haggling: wide availability of the same product, inconsistent markup and the presence of extras and services that aren't included in the asking price. First, a set of tires selling for $700 at one store might sell for $500 down the street and $450 online. Do your homework, and even print out an Internet price. Then be up front with the store of your choice about the prices you've seen elsewhere, and ask if they'll match the lowest price.
So far, this is simply comparison shopping on an item with high store-to-store price variation. But the art of haggling sometimes lies in the extras. Getting a new set of tires from the store to your car requires mounting, balancing, stems and possibly a disposal fee for your old tires. Will the dealer cover these fees? What about an extended warranty?
To bargain for extras, try sticking with the comparison-shopping approach you started with -- find out what extras other shops are willing to include, and then ask the shop of your choice to match them. Note that these extras (and shipping) can make buying tires in person cheaper overall than that rock-bottom price you found online.