Is there any problem someone who owns one house in Eretz Yisrael, selling it? (From the point that he is being mafsid his karkah in Eretz Yisrael.)
Whether it be someone who lived in Eretz Yisrael and is now moving to Chutz L’Aretz or that they live right now in Chutz L’Aretz and own a house in Eretz Yisrael and now wish to sell it.
It is permitted to sell a house in Eretz Yisrael, provided one sells the house to a Jewish buyer.
Poskim discuss the prohibition of selling land to non-Jews (question of whether this applies to Arabs), and it is clear that there is no prohibition of selling land to Jews.
Although some discuss owning land in Israel as a partial fulfillment of yishuv eretz yisrael (as the Avnei Nezer writes), this is due to economic involvement in the land, and there remains no prohition of selling the land.