Hello again, Micha. It does rather beg the question, if they're all so bad, why do you keep buying them?
I'm also assuming that the law wherever you are must be different to the UK: here, unless you're buying from a dealer (and it sounds like you are working as a dealer yourself, so there are different rules here governing trade to trade sales), the price is negotiated at the point of sale and the vehicle is legally 'sold as seen' unless a different contract is put in writing. That makes the buyer responsible for the cost of any work needed to get it to the standard desired by the buyer, not the seller.
When I sold my own Spyder, as it went for a not insubstantial price (comfortably over 25,000 Euros) and the buyer didn't have the time to view it before having it collected and transported to his private collection, I gave him a written, money-back guarantee - return the car in the condition it left me within one month, and I'd hand back every penny.
The buyer hadn't asked for that guarantee and I didn't have to offer it to get the sale, I just thought it was the right thing to do given the specialist nature of the vehicle.
The buyer kept the car and it now lives among the Gods (well, some very nice classic Ferraris anyway).
Parked outside my mate Chuck Windsor's place -
Bye bye Spyder -
Happy in its new home -
Before the buyer came up with an offer of the full asking price less his transport costs of a few hundred pounds, I had turned down three offers approaching 20k Euros from UK private buyers, and was considering offers of around 20k Euros from two European dealers, one Belgian and one French (maybe one of them was you?).
After it sold (within two weeks), an ad I placed in 'Octane' magazine (a must-read for any classic car enthusiast imho) went live (not a scam on my part, btw, it just took a month before they published my ad and the car had already sold), and I continued to receive contact from potential buyers from as far afield as Singapore for six months after the car went.
I guess, the moral of this rather lengthy tale, Micha, is that sometimes, a specialist car can be worth far more than the sum of its parts, and some amateur builders can actually put a really desirable car together., warts and all.
But then, if you really were as Madabout Kitcars as I am, you'd already know that, wouldn't you?