It's difficult to advise just looking at photos but here are my observations -:
It is an older model, not sure how old but it's certainly over 17 yrs.
It does not look as though it has had a very caring owner as the saw is very knocked about. most of us paid a lot for our Hegners and cherish them, (my Hegner has been in regular use for over 16 years and is still in immaculate condition)
You have to consider that if a saw has been knocked about as much as this has the working of it been abused too?
having said the above Hegners are very robust and will last a very long time even when they are not used by careful owners.
The absence of quick tension release will be annoying if you intend to do lot's of internal cuts and a quick release clamp is a must, you can buy a quick clamp to use for around £15-£20 but the quick tension release is not a viable option to change (it would cost too much)
The other thing missing from this saw is variable speed control, when I say missing I mean it was not fitted during manufacture, again because Hegner uses an Induction motor you cannot fit variable speed control to the saw. Many people here do not think variable speed is useful but if you are new to scroll-sawing you will find it invaluable.
In conclusion Hegner saws do command high second hand prices because they are superb and long lasting machines and they cost a lot when new so in my opinion you are better off spending this sort of money for a used Hegner (obviously providing it is fully working) than spending a similar amount on a new poorer quality saw.
If this saw was in excellent condition ( IMHO it is not) £175 would be a fair price, so in your position I would try offering £100, the seller may drop to £150 you could then counter offer £125, you get nowhere if you don't ask.
Let us know what you do.