Everything
@Chris said.
$5K is a lot of money for a non-enthusiast car that's 20+ years old now, and is anything less than perfect. One has to examine the market, and the prices which equivalent cars are fetching.
Gumtree and the likes have plenty of rough 240s with half a million kays on them, zero or little rego, and plenty of rust, yet the sellers of these piles are asking gold for sheet. And it's not only private sellers - there was a nearby MazzDUH dealer who was trying to flog a rusty POS 244 with the rot in the sills clearly visible, for nearly a grand...
Recently there was a 1995 960 wagon offered for sale here, with long rego, very low KM for its age and with all the nice factory options, and it was being offered for $2,500. There aren't many of these in OZ. The enormous load capacity of the 900 wagons plus the straight 6 engines makes these vehicles very desirable among us brick enthusiasts. Needless to say, it sold very quickly and the buyer got the bargain of the year. And that car is
arguably twice the car any 240 wagon is.
Hell, there's even a 92 model 960 wagon out there at the moment, and the ask is $3200.
That's what you are up against.
Just because the morally bankrupt can flog Toyo Choleras and other crappy Korean road gnats for crackpipe prices to bogans with more dollars than sense, it doesn't mean you're going to get gold for a 240.
IF I was prepared to pay $5K for a 240 in NSW ($3K elsewhere, due to lack of mandatory annual roadworthy inspection), I'd expect it to have under 150k, be mechanically sound, 5 speed manual, clean, un-ripped upholstery with all trim intact and the dash top uncracked, ZERO rust and ZERO body damage, a/c blowing cold and heater running hot, all electrics working, good original paint, 60% or better life remaining on the tyres, and at least 6 months rego, with no history of the car having 'lived' near the ocean.
Non-original paint loses money, unless the painter / shop is known (I have two 142s, one has had a respray; one had not until recently - guess which one has more rust issues, and guess which one looked worse before getting a birthday). Mods without engineering certs make the car of value $500 max, since then it's basically a parts car which maybe cannot be registered. Cracked / missing / non-OE trim loses money. Personalisation in peculiar tastes loses a LOT of money; if you've seen that pile which looks like an bad automotive version of a Disney movie on acid, you'll know exactly what I mean.
Of course, you'll see plenty of piles on Gumtree where they're asking megabucks, but also note how long those ads have been active...
"The difference between knowledge and wisdom: 'Knowledge' is the awareness that a tomato is a fruit; 'wisdom' is not serving that particular fruit as a dessert with ice cream."
So, yeah - there are many 240 owners (yes, I'm one) who wouldn't mind seeing the value of their cars appreciate, but you've gotta be realistic.
Good luck with sale! :)