Hi,

Difficult question.

Which type of castle? around centuries the concept has changed. So, you can find an isolated castle or a fortified city. I suppose that you mean the first, the simple castle.

I suppose that owner nobleman sells the castle to another nobleman. The possession of castle can also implicate (not always) the administration of justice (until modern age) and rents for the cultivation of land.

Consider that in late middle ages feudalism was not so stronger like in the “full” period and feudal lord lose power in front of the burghers, because the society goes to a monetary society (before was also in more part agriculture. Few money and barter). In addition, in many parts of Europe around XVI-XVII century a new noblesse was born. Not a feudal and warrior noblesse like middle ages but a category related with administration of the state, very rich and can buy castles, lands, propriety and noblesse patents. This happens because with the military revolution in Renaissance feudal lords also lose power in front of the state, represented in the figure of “prince”. In this military revolution the army (that is more largely and include poor men, not only military noblesse with armour and horse) is raised and controlled by the prince with is money, and there is no need that military noblesse raises his host.

Resume: I suppose that the castle’s market reflects the evolution of the society and economy. With a more economic society and the flourish of commerce and later industrialisation medieval warrior noblesse lost his power because they don’t have money (they don’t work, only take the rents for the cultivation of land). With this mentality it’s difficult to maintain a castle and pay taxes. So, after centuries they are economically ruined.