If you're referring to Palestinian Arabs selling their land to Jews during the British Mandate, and even earlier during the Ottoman Empire, there were indeed land sales. How many, and how much, is difficult to track. The Ottoman Empire's land records were not well-kept and well-organized, and attempts to reform and modernize the system were imperfect. In addition, there were many cases where Jews bought land from wealthy Arab landowners (or even Turkish ones) in other parts of the Ottoman Empire, which complicates tracking the question further. To make it even harder, restrictions on Jewish land purchases (i.e. Jews were discriminated against or not allowed to buy in certain areas) under the Ottoman Empire and even under British rule meant that sometimes, Jews would buy land without registering the purchase officially. Plus, there were tax incentives if you didn't register the full value or size of the land bought. So, for example, when the Jewish National Fund bought 30 square kilometers at Emek Hepher in 1929, the land registry recorded only 5 square kilometers for the sale.

Ken Stein, writing in Middle Eastern Studies, notes that sagging economic conditions in the early 1930s gave motivations to Arab landowners to sell. But how about prior, and how many did sell? Abraham Granott's best guess back in 1952 was that 73% of the land sold, was sold by large landowners and not by the relatively poor agricultural workers who sometimes owned their own land, and oftentimes simply worked the land owned by these larger owners. But Granott was a former Jewish National Fund director, so it's difficult to know if he had some motivated reasoning for the proportions he came up with, as Ken Stein notes. Ironically, Ken Stein was criticized by Rashid Khalidi, a prominent Palestinian historian, for being biased towards Israel, and Khalidi based his argument on Granott's book, while Ken Stein argued that Granott was wrong! The irony of a person using a clearly Zionist author's estimates to argue against perceived pro-Zionist bias is really quite amazing. Even so, we have to dig deeper to get more of an understanding, I just thought that was a wonderful tidbit demonstrating how complex and byzantine this whole discussion can be. The difficulty is, as Stein notes, Granott doesn't divide large landowners between those who are Arab and those who are not, though Khalidi made the claim that "large absentee landowners" meant non-Palestinian ones; in reality, that's hard to argue, since large landowning families like the Nashashibis were "absentee" landowners because they owned land in different areas that they didn't live in, under Granott's definition. Plus there's difficulty, since many large landowners were jointly owning land (as Khalidi rightly notes), which means non-Arab and Arab landowners could jointly own some of the land sold. How do you record that? Oh, and let's not forget that many Palestinian Arab land records of sales were destroyed, for fear (Stein alleges) that it would reveal that many prominent Palestinian Arabs were selling land to Jews in violation of laws and against the stigma and taboo of doing so. Stein's book, The Land Question in Palestine, actually lists many sales in its appendices and is a good read to get started on this subject regardless.

In short, this is a mess, but I'll move to other sources.

Porath estimated in 1977 that most land bought until the 1930s was bought from large landowners, Turkish and Arab alike, because the Jewish buyers preferred land that was not already occupied that they could move to and start developing themselves. The 1930s saw similar purchases mostly from large landowners, but Porath estimated around a quarter were Palestinian Arab ones selling due to debt and the economic downturn, while around 10% were smaller agricultural landowners who were Palestinian Arabs, and around half were larger non-Arab landowners. At the end of the day, it's estimated that at least 2,000 square kilometers were owned by Jews, with the land area of the entire Mandate being estimated at 26,000, though at least half of that was desert, and decent chunks were state-owned and therefore held by the British government (though there are disputes to how much that constituted). Either way, I hope you've started to understand why it's so hard to figure out how much land was sold by Palestinian Arabs to Jews during this period, and why the question is more of a dry scholarly debate with little resolution than a number we can easily look up.