If you can buy it for under rough book value and you like the particular vehicle, and it's not beat to rat shit, servicing is up to date, etc, I'd say go for it. That's a ton of vehicle for 12K anyway you slice it.
That said, you won't be making any money on it, particularily if you're putting on some miles.
The reason he is getting lots of "hits" is because people looking for vehicles are generally stupid and just see "03 4Runner V8 Limited" and "$12,000," and figure they've found and "good deal," when the price is really just reflecting the mileage. Once he tells them the mileage, most will pout because they never thought of that. Has no real bearing on the price.
With a vehicle like that, determine what YOU are willing to pay for it and offer him that number. If it's a nice looking example, it will probably sell on curb appeal vs. price alone.