My number one rule is don't look too long... And then, it's body, body, body, body, frame, body, frame. All else is easily fixed, provided purchase price is right.
But chasing rust is not my idea of fun, nor is frame damage; get under there and make sure it's straight. Generally a good idea to stay away from repaints, as they are red flags for previous accidents. Many of the Toyota V-6 engines, including the 3.0, had (and still have) sludge problems, sometimes evident when you look closely at the oil fill cover and shine a flashlight inside the valve cover. A finger will work too, but make sure to do it with the engine cold (and off, of course).
So if the body and frame are good, engine sounds and drives right, the tranny shifts as it should, and the A/C works, definitely don't wait too long. Someone else will snag it! Always lowball. Always, unless it's a sweetheart deal and you don't want to risk rocking the boat! Don't be ashamed, they'll only laugh at you for five minutes after you've left, and you'll probably never see them again anyway. You can use verbiage such as,"I sure don't want to insult you, but the most I could possibly offer you would be (roughly 60-70% of asking price, +-). You can always pay more than you say, but a private seller will seldom take less than you've already agreed to pay.
Welcome to the mud!