The P's and Q's are honest airplanes and a bit of a sweet spot of the 182 line.
Things to have on your inspection list
When where the fuel bladders last changed. They have about a 10-year lifespan, and about $5,000-$7,500 to replace depending on shop.
Engine inspection. Compression numbers are easy to obtain, but borescope images are going to tell the complete story.
When was the prop last dynamically balanced? 55WB that
@JCranford and I fly had it done 8 weeks ago andit made a huge difference. The slight out of balance caused premature wear in the engine mounts. And check the engine mount condition too.
Does the aircraft posses the Trolltune gross weight increase? This is a paperwork only thing that ups your MTOW an additional 150 lbs.
www.182stc.com
Can the seller produce the oil analysis records. This, in addition to other inspection items, can provide detail,about the health of the engine.
Only other items I can add is the thorough logbook review for AD compliance and items that are recurring a bit too often, and a thorough inside the structure inspection for corrosion.
If the one you have your eye on works out, you will be getting something that can serve you well for a long time.