In case the seller or an apartment has already moved in or has rented out the apartment and got the woodwork already done, then one has to evaluate a few things to put a value to the investment that the exiting seller has already invested. While there is no steadfast rule or a thumb rule to evaluate the cost of interiors done by an existing owner, one should really look at it from a utility point of view and then make an offer. In case the existing setup works for the new buyer, he should be able to to put a slightly higher value for the interiors/woodwork etc. In case it doesn't, then a lower value.
Apart from this, the other factor that one should consider is cost of time, for e.g. in case as a new buyer you would like to take possession of the apartment and move in asap, then you should be looking to pay a fair value for the assets and use it to your advantage.
Generally speaking, the value that one does get for interiors and woodwork done is definitely never equivalent to the moneys spent, it will always be lower, in fact, substantially lower.