Beware of things sellers may say that could allude to poor maintenance or abuse.
Things like "boy I neva change nuttin in dis car! it cud real tek jammin'!" don't bode well for the condition of a car.
Things always need periodic changing in any vehicle, from fluids and filters with short change intervals, to parts with longer change intervals like suspension parts, engine mounts etc. If a seller "neva change nuttin" in his car, that doesn't mean the car never needed it changed.
And well, "it could real tek jammin" could suggest plenty fyaz was geed. Beware of the condition of your rotating parts.
Case in point.
A co-worker the other day was boasting about how he never change anything in his L-Touring and some other sheit about the oil in there over a year now (he driving from Woodland to Piarco daily eh...ah glad he changed tyres at least!) and how the car "still going strong". He keeps it clean and from the outside, the car appears to be in mint condition.
But guess what. When you drive it, even though the car feels loose and unstable, the engine is sluggish and slow to respond to throttle changes. Body and interior good, but engine, drivetrain and suspension in a mess.
Have a trustworthy mechanic (I know
oxymoron, but humour me here) inspect the car and you two take it for a test drive. Listen out for noises. Look out for leaks. Crud on the outside of the engine, rust in the radiator overflow, black brake fluid, thick oil and brown/burnt transmission fluid are all signs of poor maintenance.
If "de a/c jus need a lil gassin' up", that prolly means it'll cost you a mint to fix it. Because if it were that simple, there's nothing stopping the seller from investing a couple hundred to gas it up themselves before showing it to buyers.
Lastly, bear in mind that even with regular maintenance, engines wear and metal rusts. Rings wear, bearings wear (esp if fyaz was geed), seals get hard and lose their ability to stop oil, hoses get soft, vacuum lines get leaky. Inspect all these things before deciding on your purchase.
If you've already made up your mind to swap or rebuild, then take stock of what's gonna be left when you tear out the old engine and see if it's worth the time and money to get it to where you want it.
You don't have to jump out all that pesh in one go tho. My first car was a rusted, beat out old EE80 hatchback that get real luvup over the 4 years I had it and by the time I was done, it was in mint condition before it was sold.
Ultimately, it's up to what you can handle.