Ok, lets get to helping you out here, you've stated that you're not a "pin guy" so you have come to the right place for help. However a little research is needed first:
To begin, we have a thread on here called "How much is this table worth?", you can find it below:
http://www.pinballinfo.com/community/threads/the-how-much-is-this-table-worth-thread.5286/
Posting in this thread asking the percieved value of a NIB Hurricane would have been a grand place to begin and you would have been advised on a more realistic price point than £7000
Despite the fact it is NIB, as Carl has said, there is a fair chance the 25 year old batteries have leaked causing god knows what level of acid damage to the CPU (and possibly other) boards. These are not cheap to replace.
Also, where has it been stored for the past 25 years? Was it possibly damp or humid?
You say that:
The pins however oll play with a ball, shoot the ball out almost the same way, have flipper-fingers, drop targets, bumpers, ramps they even copied that DMD´s one company from the others.
A little research goes a long, long way here not just for talking about how they play but also the value of pinball machines. If you had a NIB 'A' listed Bally Williams title (lets say Addams Family, Attack from Mars, Monster Bash, Medieval Madness), these are worth a heck of a lot more than a NIB Hurricane would be due to their popularity, quality and demand. You might Hurricane and fair play if you do, we all have different tastes here but it is not a top rated machine in any quarters.
You say that someone has offered you 4000 euros, that equates to around £2800 which is well short of the £7000 you ask for in the original post.
There is a lot of information online with getting an idea of what a pinball machine is actually worth but putting a seemingly random value on a machine that is not universally popular and expecting to sell it here, where the majority of members are "pin heads" and know the rough value of machines wont go anywhere.
I wish you well in your sale (especially because Vienna is such a great city full of great people) but please don't expect to get that sort of money unless it is from someone who has lost their marbles or has no idea the actual value of a pinball machine.
Regards
Ian