75k and 105k is fine for a 99-01 v8 explorer ... Sounds like the guy cleared the code and tried to sell it before it came back. Find out what the code is. You might be able to get a great deal on it. In California a 99-01 limited in excellent condition would be around $5k-$6.5k. I found a 01 Limited with 100k miles for $4k...He was asking $5.5k What are they asking for these?
The one with 75k was a 2001 Explorer XLT (pretty basic). It was rough on the inside (read: trashed). Exterior was OK. Brakes/tires seemed ok. Some obvious paint repairs due to rust, especially on the bottom of the hatch. Motor/trans sounded fine and ran strong, but about halfway through a 15 mile test drive a code was thrown (it was the "Service Engine Soon" and not "Check Gages" light). The stealership was asking $8k.
The other with 102k was a 2000 Mountaineer Premier. It was immaculate inside and out (aside from minor wear/tear-it's a 2001), fully decked out, and ran great. Brakes were good but the tires looked like they only had one more season left in them. It sounded like there was a slight exhaust leak, though. The rear driver's side door wouldn't open from the inside (I checked the child safety lock-didn't help) and the front passenger door lock actuator sounded like it was ready to go. This stealership was also asking $8k.
For comparison, the wide variety of others I have found (but not driven/seen): 2001 Ex EB/106k/$8k, 2000 Mt Prem/123k/$4k, 1998 Mt/109k/<$5k, 2000 Mt Prem/90k/$7k, 1999 Ex EB/127k/$6k, and a bunch more. In fact,
here's the AutoTrader list that I'm pretty much working with. Cars.com and Craigslist don't really offer as much as AT.
Tanks, good motors, good transmissions and good transfer cases.
Our 99 Eddie just turned over 200k and has aged very well, it still looks great the paint is bubbling a little on the inside lower rear doors a bit due to rust but no rust on the exterior I am happy for that.
And with good tires in the snow, virtually unstoppable as snow goers go.
I would say common problems include exhaust leaks, failed radio displays, wheel bearings, ball joints, rear wipers, door latches, door lock actuators. Some of those things are over rated. My rear wiper is cashed and the radio display goes out intermittently. Its also common for used cars to need a brake job or 2 in the coming years, many also have junk tires.
They also have very complex piece part exhaust systems (read: $$$) so you may want to avoid that as I have heard some junky sounding ones running around. My exhaust is in damn fine shape for 200k I'm very pleased with that and the heated seats make it a preferred ride for me.
We also have a 99 Jeep Grand with 193k on a 4.0 and that is also a darn fine truck, but its no V8 Eddie Exploder. I will say the Infinity stereo in the Heep is better.
I planned on replacing the radio with an iPod ready unit, so that's not a big deal to me anyway. The other items are of concern to me and I do my best to see what's wrong. I really haven't got the slightest clue on how to tell if a wheel bearing or ball joint is good or bad. Again, I'm not mechanically inclined, but give me enough time and I can figure it out. (I'm an Electrical Engineer, if that explains my lack of mechanical knowledge...

)
I do like the Jeep 4.0 motor...when it's in a Wrangler. I test drove a GC with a 4.0 and it felt a lot like an Explorer with its 4.0...anemic. I like power. *insert Tim Allen grunt here*
Got 199K miles on my '97 and it's still going strong. The AWD is great! The off-road guys don't like AWD (cause there's no low range, I guess), but for public roads, both paved and dirt, I don't think you can beat it. The 5.0/4R70 drivetrain is practically indestructible. The heat is hot in the winter, and the A/C works better in the summer than some new cars I've ridden in.
As for problem areas with the 2nd gen's - lower front ball joints. But that's a $35 part and about 1.5 hours labor each side. They tend to rust first in the back of the rocker panels, directly ahead of the rear tires. Stick your head underneath to see what's going on - if it's got running boards, you can't see the rust from above.
Door latches/power locks also tend act up due to corrosion inside the latch, but that's a cheap fix as well. I got all 4 latches on ebay - they were salvaged from an Ex in Louisiana where cars don't get eaten by road salt.
I would like to get into offroading some time in the future, but right now my fun stays on the streets.

I got some buddies down in Louisiana. Maybe I can get some of them to visit some junkyards for me, if needed.
Like other people have stated this is a great engine and drive train combination. The major repair costs that I had start cropping up around 145,000 miles were:
CV-joint on aft portion of front driveshaft where it connects to the transfer case failed. Cost: $160 (Re-manufactured shaft from Advance).
Starter motor internal failure of some sort. Cost: $330 (Dealership replacement because it was snowing outside...).
Alternator internal failure would not provide proper voltage. Cost: $150 (Got a new battery for the hell of it add another $100).
Camshaft position sensor stator broke off inside sensor housing. Cost $60 (Re-manufactured from Advance).
Rear wiper and fog light switch broke off center console. Cost $5 (plastic epoxy to reattach).
Dashboard back lights progressively fail. Cost $10 (10 pack of #194 bulbs at Napa).
Front upper and lower ball joint boots fail and eventually cause bearing failure. Cost: $500 for both and new cam bolts (Give or take a hundred).
Driver's door handle looses spring tension. Cost $0 (Ignore).
Passenger rear interior door handle broke. Cost $0 (Ignore).
Radiator leak from plastic tank to aluminum core seal failure. Cost $160 (New from Advance).
Cruise control rubber buttons tear on steering wheel. Cost $0 (Ignore).
Resonator on tailpipe leaking. Cost $70 (Local muffler shop replaced with pipe).
Spark plugs and wires. Cost $80 (Autolite double platinum and wires from Advance).
Fuel filter and air filter because they needed it. Cost $30.
Keep in mind that all these problems occurred over the course of two years giving me ample time to fix them on a budget. One major thing to note about that is if you ever do your own maintenance you'll start to appreciate how much room there is to work around in these things. If I had to do it again I would still buy it. You just can't beat an AWD V8 with snow chains in the winter.
I do intend on doing most of the work myself, so this list does put the various issues in perspective. Given that I do about 20k miles a year and hopefully I can find one with close to/less than 100k miles, I should be in good shape for at least a year (I hope) but you never know.
/Wow, long post was long.