Advice on buying a Gen II Prius

You'll get lots of suggestions here on this one. There are many folks who have hit 200k+ in their prii so 100k isn't the be all end all it used to be. As long as the car has been cared for (which most prius owners are sticklers about caring for their car) you should be in pretty good shape.
We lucked out when we bought our 2005 a month ago as it was a one owner and had all work done at the dealership which means there are logs of work done.
Put in the VIN number of any prius your looking into at Toyota Owners Official Website: Service Coupons, Owners Manuals ... website. You can view all work performed by TOYOTA at this website.
Gen II had some problems with the water pump, there was a recall on them, check to see if that was done using the website mentioned above. As well as floor mat recall, and steering shaft/column recall.

If you buy from a dealer I'd try these things
1) ask them to do a diagnostic test on the hybrid battery and give you the results. Chances are they may have done this but ask to see any results or paper work on this test.
2.) Ask them for a bottle of touch up paint. Hey why not leverage your power and get some touch up paint in the process, its like $10 but get a bottle and some clear coat so you can keep your new used car looking awesome.
3.) Ask dealer to check/verify/service HID leveling sensor if the car is has HID headlights, the sensor has a tendency to stick and require complete replacement at to the tune of about $300 for the part alone.
4) Ask dealer for approximate/actual age of 12v battery, and request a new one be installed if its more than 5 years old. They're not like most other 12v batteries, and run from $150-$250 for the battery alone. So ask about it.
5) Check the toyota owners website to see what maintenance should have been done for the car milage and ask the dealer to get it all up to par, transaxle, coolant, oil, filters, etc. Again chances are they've done an oil and filter change but ask and looking transaxle and coolant changes and other required/recommended service for the cars milage.
6) Carefully check the gear shifter, some shifters develop a click or stickiness to them. This can be an easy fix if the plastics on the back side are warped or can be a $300-$900 fix if the shifter actually breaks. Inspect it carefully and be picky.
7) I'm sure there are some other specifics to look for I've only had my 2005 for a month and these are the things I've learned since then,

Other than these things just your normal used care buying tips apply
1) test drive it. take a friend with if you can and let them drive to get their impression of the way it drives and handles
2) carefully inspect all electronics to make sure they function properly
3) if possible arrange to take it by your local mechanic to get their trusted opinion on it.
4) Don't rush into buying anything. You have a car now, so take your time
5) don't be afraid to walk away.

These are very dependable cars and with the proper car and attention like anything else they'll last just about as long as you want them too.

 

I don't know where you are but, I bought mine from Steve @ Autobeyours.com. He rebuilds salvage vehicles and is an expert. Mine is an 06 and it drives like new. I know there is a lot of hesitation about buying salvage but, I am glad I bought from him. Check it out if your close to Scottsburg, IN.