Welcome!
Things to look for are these but not limited to as others may have advice too.
Check if , swirl flaps have been replaced recently . gearbox regularly flushed and if a tow vehicle maybe a rebuilt gearbox is in there , rear diff needs bearing replaced with a proper one at anything from 60,000 to 200,000k so look to that , engine mounts are all replaced as well as others on driveline , auxiliary belt has been replaced twice , aircon compressor isnt noisy , should have been replaced by. now . radiator fan unit with controllers is recently new or has been done , the steering lock control module fails as do the ignition slot motorised fob thing in dash ( dont ever push it all the way in , J U S T in is enough or if proximity fob then dont put in dash slot ) various window switches and random getting stuck and doing their own thing needs reset and more at some stage I dont know what , there has been a recall on seatbelts as the lap sash has a pretensioner in a dumb spot just where you sit when getting in as it stays in the way if you dont push it back on its swivel , I myself WANT a seatbelt pre tensioner and as the recall removes it and bypasses it the recall is making the car less safe! ( they have had some go off by themselves from people sitting on them all the time , im taking the chance) Usual suspension and bushes , springs no doubt , you can upgrade brakes at front I believe with XC60 larger. discs and callipers swapped in if you feel the need. You should get one with Dynaudio sound system , it is brilliant , dont fret about Bluetooth or navigation , get a car audio place to put a proper system in , even with CarPlay or android auto ( I hear CarPlay is rubbish....) using a large/ish tablet type device mounted on dash so you get modernity as all the Volvo stuff for BT and NAV is junk now.
we have an S80D5 2009 and at 120,000k it needs swirl flaps , a $1200 job , id delete them but its a bit involved in the cars brains. The EGR SYSTEM PIPES should have been regularly cleaned out and low soot oil ALWAYS used , if its a city car it MUST be thrashed a lot or it will have led to much carbon buildup in motor I imagine (the missus is a racer driver from turn of the key in any car so its staying carbonless to a degree) but the swirl flaps are damned plastic , so stupid a design , Ford owned Volvo too bloody long! And we pay for their cheapness!
Prime example , my V60T6 has the same Haldex rear diff as the S80 AWD and XCs and the main bearing is too small and made in India and Germany so far as my local Volvo Independent shop has found , they are Bothe junk bearings! YET! The same portend diff is in Landrover ( which Ford owned at the same time ) yet you use a LR bearing to replace the dead one as Volvo would charge for a whole new Haldex diff at a price maybe as much as your car........now , LR make their own bearings...................)
Im tired from city driving so rambling on , tell me if makes sense , really , get an INDIE. Volvo guy to check or look and ask back here.
If they say regularly serviced and none of the above can be proved then the local hack has changed the oil and replaced bits as they break , and the car would need to be just about FREE if thats the case as you WILL spend for all of the above way more than buying a newer and better 2011 or whenever the last ones were model.