You keep saying "we" but are you OP? And I didn't say anyone should throw away the money, irrespective of how much they earn. Nor I am saying OP is getting a great deal here. All I am saying is -

If apartment costs 1900 EUR cold rent, then there is a good chance that the furniture used is some expensive ones as well (probably because previous tenant can afford it?). OP should evaluate whether they like the stuff they are getting for 12K & what is the current fair market price. And take the difference & see if it is worth getting into this deal. A good kitchen on IKEA is already above 4K & that's without installation cost.

And given the current market conditions, 12K might not be a fair deal for a used kitchen for the OP, but pretty sure there are many in this housing market who would be happy to pay for it.