Should you swap a laptop for sale on ebay?

I would like to sell or exchange my laptop on ebay. I already have a prospect and I wonder if I should sell it because of my data. I used to use it a lot in the past and had a lot of data on it. Could you restore it or hack the laptop and get it all done?

So the safest thing would be to write to the customer that he comes without Windows 10 and format it before sending.