I think you'll get a bias towards stories where there were (ultimately) extenuating circumstances here OP. I don't hink it's the norm to sell for drastically below asking, especially if it's a popular area, or the work is mainly cosmetic.
We've been house hunting for at least a year, and I keep a through track of sold prices for anything we have put an offer in on or viewed. Not seen anything yet sell at any comically low amount. It's usually about what you'd expect- around 5-15k off asking.
With that said, he only things I've noticed sell for their asking price are those that are cheap for their area (worst house in a nice road) or the decorative order is so good you can just move in (fresh plaster, new carpets, newly fitted kitchen/bathroom etc)
With all that said, I'd just advise checking the sold prices for the postcode (google it), check for listings of neighbours houses to check condition and prices. If it hasnt been decorated in recent years do a proper survey if you have an offer accepted to highlight any hidden costs for repair, electrics, damp, boiler etc. It is only a bargain if it is still one after that extra cost.
I would go in low with an initial offer, they'll more than likely reject it anyway. Raise it a bit and then play the waiting game, butter up the estate agent etc- they will know the vendors situation and we have found that though they work for the vendor in technicality, almost without exception they are out for themselves and want to secure their commission- they want it sold.
I wouldn't expect to get it for anything remotely under 200.
I've just left an expensive part of the SE to buy (in a less expensive less desirable part of the SE). The asking price was 190, we offered 170, they rejected, settled on 175, then reduced it to 172 when the survey found an issue (5k repairs, wesplit the cost) so really its 175 either way you look at it. Still a decent price for a family home in a nicer road for the area, good schools etc. Decoratively a state and we gave limited funds but will get there over the years I'm sure .