There are not many options. If you can get the house at the estimated price without an agent, that is already great in the current market situation.
If it seems too expensive to you, of course you can also make a lower offer to the seller and hope that you still get it.
It naturally depends on the relationship you have with the seller.
If the seller wants to sell the house to you because he knows you or something, he might come down a bit on the price.
If the seller wants to sell the house at the highest possible price, then your chances are slim.
If the seller also gets an offer from other interested parties that is perhaps even above the estimated price, the outlook is bad for you as well.
I would say if you like the house and can afford it, then buy!
Maybe sell the condominium in a few years and use the money for special repayments. Then the remaining debt after 20 years should also be significantly smaller.