Selling an 05 suburban with 240k miles for 3k
240k is a nice amount.
And 3k is asking for a lot being that it's 14 years old.
That means the engine, transmission, tires,rotors, brakes, suspension might need some tune ups, whether the tie rods, leaf springs, list goes on.
And not to mention the ac system, hoping it's running fine.
Not to mention the spark plugs and wires, and flushing all the fluids on a 14 year old car.
Now if you wrote....
Selling an 05 suburban with 240k miles for 3k, well maintained, serviced it at the Correct intervals as recommended in the manual. Good tires brakes and transmission ,engine.
Then I would say for 3k there's "something" to talk about or negotiate...
Good luck!