Averages of a population of used examples of any model are not that useful to individual car buyers because you are only buying one. If you were buying 1000 Sequoias for some business, then it would be more useful. According to consumer reports, these have worse than average problems with drive system, brakes, body hardware, and power equipment. Because every used car is different, a complete inspection by your mechanic is necessary. Only then would you have the data necessary to know if the car was worth buying at any price, and how to begin your negotiation. This particular one is grossly overpriced if its one of the lower trim models. Asking prices are usually pure fantasy. If it passed a mechanical inspection, you would need to negotiate for a final price. I've never paid more than 67% of asking price and have bought many used cars at 50% of their asking price. I've also walked when the seller wasn't interested in doing business. BTW, Toyotas don't run any longer than anything else. How long a car lasts depends on how it was maintained and driven, not the label on the back.
Used car dealers buy at auctions. Their cars usually come from trade-ins at new car dealers when it had too many miles for the new car dealer to put it on his own lot, or if repairs would be too costly for the new car dealer to sell it at a profit. New car dealers keep the best used cars to sell themselves.