A couple things...
1. Having owned a 2003 Supercharged Frontier, I can say that while this generation of Nissans is fantastic, I'd much prefer the naturally aspirated VG33E over the supercharged ER version. I got absolute garbage fuel mileage (like around 10) on 235/85s and with a roof rack. I do suspect a large amount of that had to do with the roof rack, but it is something to consider. Might not be as big a deal if you don't plan on lights above the windshield or an aftermarket rack. The claimed 18 mpg in the ad seems way high to me with bumpers and sliders. I'd guess he's averaging 16-17 MAYBE, but the 18 sounds pretty high.
2. The VG33 engines are also known to have a knock sensor that likes to crap the bed fairly often. When this happens, the engine thinks it's pinging and changes around all kinds of things, which causes you to run rich and get bad mileage. It's especially bad in the supercharged engine because the SC adds a bunch of drag on the belt. When the engine is in normal operation, the supercharger adds power so it kind of balances out. When the knock sensor dies, the supercharger still creates drag, but it goes into bypass mode and opens a valve that more or less renders the supercharger useless. So once this all happens you get atrocious fuel mileage, which stings even more because you're supposed to run premium fuel in the SC engines. All that being said, the knock sensors aren't exactly expensive and changing them isn't too terribly bad if you're pretty handy. There's also a mod that allows you to relocate the knock sensor to on top of the intake so that next time it goes, it is super easy to change, and theoretically it still operates as normal. Some people say there's more of a risk in this mod with the SC engine, others say it's just fine. I've yet to hear of someone wrecking their engine because of this though. Ask about the knock sensor, whether it has been replaced and/or relocated. Normally I'd say this isn't likely but this one seems pretty well modded, so who knows.
3. Also, one other thing to really be aware of is the longevity of the superchargers themselves. Generally, they go out in the neighborhood of 100k miles. Seeing as this one is at 103k, it's worth asking if it's the factory supercharger. If it's not, you may be in for a fairly hefty repair bill. Mine cost me about $1200 to replace. When they do fail, they tend to go catastrophically. The bearings seize up or something stops spinning right, and the belt gets a huge amount of stress put on it. The belt will then snap and take out the other two belts with it. Ask me how I know
If you want to avoid all the potential problems with the supercharger, you can bypass it completely by removing the belt, but then you bypass the AC as well. I wanted to look into getting a belt to just run the AC, but I sold it before I could find a solution. But then you don't get the super cool SC whine and the extra 30 HP.
4. The only other thing to be concerned about with the VG33 is the timing belt. It is a rubber belt, and the engine is an interference engine, so if you snap the timing belt while it's running, the pistons will ********** into the valves and wreck them. Luckily, the timing belts usually last about 100k. Check if it has had a timing belt replacement. If it has, awesome. If not, they are kind of a pain to do.
5. ARB never made a rear bumper for the Xterra. That one looks like a Shrockworks to me. Still a fantastic rear bumper that will last forever though. And the front is definitely an ARB, which is a great bumper.
Otherwise, it looks to be in exceptionally good condition. Nice and clean, doesn't look like any body damage, and the interior looks pretty good. I see it also has rock sliders already, which is an awesome plus. Even better if it's got skids already too. Those look like Hella 4000s on the front, which are great lights. Overall it looks to be a really clean truck. The price is pretty damn high though, considering the KBB value of around $7k in your area of Oregon. The extra mods will add a fair amount of value, but not $2500. In my opinion it's worth a look, but you'd have to play hardball to get it for a more reasonable price. If it was me, I'd feel more comfortable around $8500, but it's worth a shot talking to him if you really like it.
At that price though, you're fairly easily within reach of a 2nd gen Xterra, which is an amazing leap above and beyond the first gens. Much more power thanks to the awesome VQ40, more space, better looking, more comfortable, way better fuel mileage, quieter on the road, softer suspension, nicer interior, better suspension design. Take a look at those rigs while you're looking, I think you'd be much happier with one of those for that price.
Best of luck!
